New XP client...HTTPS: Request time out? Help!

[spaky]

Https = Request time out

I am preparing a client-migration from Windows 98 to
Windows XP.
Through the internet my users can login on a "HTTPS:"
website and
to make use of a web-administration application.
Under Windows 98 everything goes ok BUT under Windows
XP not..I got a "time request out" (everytime). I think
that the problem is the Windows-policies BUT where should
I looking? and how can I test this on my client and after
make the changes on the domain controller?

Spaky