Contributed By: Sudheer GN [MSFT]
As part of XPSP2 RC2 release, BITS 2.0 RC2 version is available for download to XP RTM/SP1 machines.

Please see:

http://www.microsoft.com/technet/prodtechnol/winxppro/maintain/sp2wuins.mspx

for the procedure to download new Windows Update V5 client and BITS 2.0 to a XP RTM/SP1 machine.
You can choose not to install XPSP2 after installing BITS 2.0.

Please see the warning on the page. (WARNING! This technical preview is unsupported and is intended for testing purposes only. Do not use in production environments.)

If you find any issues with BITS 2.0, please post them to the microsoft.public.windows.backgroundtransfer newsgroup. To find out what is new in BITS 2.0, please see:

http://msdn.microsoft.com/library/en-us/bits/bits/what_s_new.asp?frame=true