winxp ras client doesn’t register in DNS on W2003 RAS

Hi,
my wixp clients doesn’t register in DNS when they connect via VPN (w2003 RAS, ISA 2004), they get IP and have the DNS in their settings, but still I can’t ping the client’s pc-name only on IP.
Clients register just fine when they connect internally and then I can ping on pc-name.
When I look at hte records in the dns there is no record from the clients connecting via RAS, only internally.
There was a settings in ISA2004, but I can’t find it now after patching up the ISA…
Everything else works fine….
Anyone any ideas?