do a complete reinstall from a normal XP cd (not the recovery bull), do not use partition magic, join all the partitions into one (or create several, depends how you store your data) using the XP installation CD and make sure they are NTFS.
then do the installation of XP and then download and install stock acer drivers from their site.
then install a firewall and antivirus proggie of your choice,
adaware and spybot if you happen to get loads of adware/spyware (porn browsing again?), as well as mozilla firefox for browsing and thunderbird for mail.
the rest are the programs of your choice.
After this your system should be stable and fast for at least 6 months.
I do this on every laptop/desktop i owned, never had any major problems, and i never get infected with adware or viruses unless im really unlucky, in which case i usually get annoyed pretty fast and do a complete reinstall again.
if your a total noob get a geek friend to do it for you