There are several things you can do. Disabling, or removing components for
services that are not neccessary is one way. Disabling DHCP, or setting a
static IP if your network does not have a DHCP server. There are also some
articles on http://www.microsoft.com/windows/embedded/community/tips/xp/default.asp.
Namely the articles by Andy Allred about device pruning, and reducing
runtime image size. These should get you started and I'm sure others will
have more suggestions.