Sinky, are you running Norton AV?
Get this all the time on the dialup support desk, theres a prob with Norton 2000/1/2/3/4
http://service1.symantec.com/SUPPORT...01060516275506
Follow the details (disable email scanning, restart the computer, enable email scanning) then try it again. Should be ok then.
On the browsing speeds, contact technical support (0845 650 0121), it may be a single user issue (ie. ur signal strenth has dropped), and it aint gonna get fixed until you report it.
ps. XP SP2 is excellent for me, best beta I ever installed, made my wireless connections so much better (and easier to manage) than they were.