In any XP installation I do, I always do the following to speed up network browsing:
Network-Disable administrative shares, ($C, etc, etc):
Network-Disable restoring mapped network drives on logon:
Network-Disable automatic search for network folders and printers:
Network-Disable Look for Remote Tasks, (XP looks for Scheduled Tasks on any network PC you connect to - WHY?????):
I also do a few other network tweaks either applied via nlite or a file of reg tweaks.
Obviously, don't apply them unless you know what you're doing, (not directed at anyone just the usual boring disclaimer), and don't apply one if you don't want to disable that functionality.
EDIT: For some reason I had an extra line on the last reg tweak - silly me