Here's for Whistler: https://winworldpc.com/product/windows-xp
and here's for Longhorn: https://winworldpc.com/product/windows-longhorn-vis
Or you can try ftp://old-dos.ru/OSCollect/OS/Windows/Betas --> Username: oscollect, Password: oscollect
Please note that these versions of Windows are unstable, and graphics may not display properly. Use a VM or an unused PC/laptop to try them.
Additionally, here's the best builds for Whistler and Longhorn (those with the most major and/or visible changes):
Whistler 2296: https://winworldpc.com/download/4235D4B7-18DA-11E4-99E5-7054D21A8599
Whistler 2410: https://winworldpc.com/download/42138015-18DA-11E4-99E5-7054D21A8599
Whistler 2416: https://winworldpc.com/download/422037D2-18DA-11E4-99E5-7054D21A8599
Whistler 2419: https://winworldpc.com/download/4227C7BC-18DA-11E4-99E5-7054D21A8599
Whistler 2428: https://winworldpc.com/download/420FAEA7-18DA-11E4-99E5-7054D21A8599
Whistler 2475: http://goo.gl/Vt9QkG --> Username: oscollect, Password: oscollect
Whistler 2481: https://winworldpc.com/download/420BDCF8-18DA-11E4-99E5-7054D21A8599
Longhorn 3683: https://winworldpc.com/download/426256FD-18DA-11E4-99E5-7054D21A8599
Longhorn 3718: https://winworldpc.com/download/42756971-18DA-11E4-99E5-7054D21A8599
Longhorn 4008: https://winworldpc.com/download/426F0DB5-18DA-11E4-99E5-7054D21A8599
Longhorn 4015: https://winworldpc.com/download/426C834F-18DA-11E4-99E5-7054D21A8599
Longhorn 4029: https://winworldpc.com/download/427D0CDA-18DA-11E4-99E5-7054D21A8599
Longhorn 4039: https://winworldpc.com/download/425E870A-18DA-11E4-99E5-7054D21A8599
Longhorn 4042: https://winworldpc.com/download/428D924A-18DA-11E4-99E5-7054D21A8599
Longhorn 4051: https://winworldpc.com/download/426B3DBA-18DA-11E4-99E5-7054D21A8599
Longhorn 4074: https://winworldpc.com/download/4264E214-18DA-11E4-99E5-7054D21A8599
Longhorn 4093: https://winworldpc.com/download/4297C0D6-18DA-11E4-99E5-7054D21A8599
Also, if you're asking for product keys (legal, since these are abandonware), and date and time to install these (since these versions of Windows are meant to be installed on certain dates only):
Whistler:
2202: 02/03/2000
2211: 03/10/2000
2223: 04/12/2000
2250: 06/29/2000
2257: 08/11/2000
2267: 09/11/2000
2276: 09/29/2000
2287: 10/13/2000
2296: 10/25/2000
2410: 12/09/2000 F6PGG-4YYDJ-3FF3T-R328P-3BXTG
2416: 01/05/2000
2419: 01/14/2001 RBDC9-VTRC8-D7972-J97JY-PRVMG or DW3CF-D7KYR-KMR6C-3X7FX-T8CVM
2428: 01/30/2001 DTWB2-VX8WY-FG8R3-X696T-66Y46 Every build has the same product key until 2454
2430: 01/31/2001
2433: 02/07/2001
2446: 02/25/2001
2454: 03/07/2001
2457: 03/10/2001
2458: 03/10/2001 RBDC9-VTRC8-D7972-J97JY-PRVMG or DW3CF-D7KYR-KMR6C-3X7FX-T8CVM
2462: 03/16/2001 Personal: Same as 2428, Professional: Same as 2458
2463: 03/29/2001 Same as 2458
2465: 04/13/2001 Personal: Same as 2428, Professional: Same as 2458
2535 and 2542: BX6HT-MDJKW-H2J4X-BX67W-TVVFG or VQP4F-V47P8-BBDXK-R7K9Q-B42BB
Longhorn:
Product keys ("set date to" is available below):
3863 until 4029 (except 4028) 4028 is part of the next one
CKY24-Q8QRH-X3KMR-C6BCY-T847Y
4033 until 4093 and 4028
TCP8W-T8PQJ-WWRRH-QH76C-99FBW
BIOS Dates:
3863: September 23rd 2002
3706: October 29th 2002
3713: November 13th 2002
3718: November 19th 2002
4008: February 19th 2003
4011: March 5th 2003
4015: March 28th 2003
4028: July 1st 2003
4029: June 29th 2003 (That may be confusing how it's a higher build number but earlier, don't worry)
4033: July 17th 2003
4039: August 27th 2003
4040: August 29th 2003
4042: September 9th 2003
4044: September 17th 2003
4051: October 1st 2003
4053: October 22nd 2003
4066: February 14th 2004
4074: April 25th 2004
4083: May 16th 2004
4093: August 19th 2004
BONUS
Windows 7 Beta build 6780:
32-bit: ftp://old-dos.ru/OSCollect/OS/Windows/Betas/Windows%207/Windows%207%20Build%206780%20Enterprise.rar
Username: oscollect
Password: oscollect
Set date to: 30/08/2008
When it asks for a product key, just click "Next".
Windows 7 Beta build 6801:
Install guide: https://www.youtube.com/watch?v=qBr6jgJvLyQ
32-bit version: http://bit.ly/WIN76801
64-bit version: http://bit.ly/WIN76801x64
Set date to: 9/14/2008
When it asks for a product key, just click "Next".
Windows 7 beta build 7000:
Install guide: https://www.youtube.com/watch?v=Zu7qO3JG9_A
32bit: https://mega.nz/#!VN9FHBrB!pxOSell1sEy3vVsW5QqKUcs8ZjAX7piKlNZkSykf5-I
64bit: https://mega.nz/#!tIFlATQY!H3NKB2ENtUCoik4yzeiIPNJGSyLG4G6kb3JtXlGrlvQ
Set date to: 12/13/2008
When it asks for a product key, just click "Next".
Windows 8 build 7850:
Install guide: https://www.youtube.com/watch?v=2STbMSDbp-E
32bit: https://mega.nz/#!gUt1zACJ!nYGDel9ipsD3jneEQda-CFngwK87r4AIXHqCQMV83to
64-bit: https://mega.nz/#!0IUzTb5K!RSAJscFZnOBSXgT7sqjV-ym06M9Yfse7kZNWIMK2d9M
Set date to: 09/23/2010
Windows 8 Dev Preview build 8102:
32bit: https://web.archive.org/web/20120111050232/http://wdp.dlws.microsoft.com/WDPDL/9B8DFDFF736C5B1DBF956B89D8A9D4FD925DACD2/WindowsDeveloperPreview-32bit-English.iso
64bit: https://web.archive.org/web/20120111053021/http://wdp.dlws.microsoft.com/WDPDL/9B8DFDFF736C5B1DBF956B89D8A9D4FD925DACD2/WindowsDeveloperPreview-64bit-English.iso
64bit Developer: https://web.archive.org/web/20120111055420/http://wdp.dlws.microsoft.com/WDPDL/9B8DFDFF736C5B1DBF956B89D8A9D4FD925DACD2/WindowsDeveloperPreview-64bit-English-Developer.iso
Set date to: 31/08/2011
Product Key: 6RH4V-HNTWC-JQKG8-RFR3R-36498, But it's not needed during installation