DC Relay or Proxy?...

I am a litle dum today, but.... what is the best way to create a 'sysvol relay' without instaling a domain controler? Im having problems with xp clients over a 2003 network, sometimes they just dont aplie part of the policies, others it take a long time to process logon script... I havent created it, but it would bee nice to find a way to get a 'dc relay agent' or something, couse the 'slow link detection' is already off, and still happens a lot, because of a wan 128 k conection...
Could it bee possible to use something like a proxy - isa server?

Any help would bee nice ;)