Hi,
if your computer is new and it is slow already I would run these programs and probably remove everything they find. Run them once each, reboot and then run then both again just to be sure:-
SpyBot S+D
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AdAware
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Then make sure you have a decent firewall and antivirus program which you update on a regular basis (once a week is good, but once a fortnight is a must).
I recommend these 2 free programs, as I install them on clients computers when they have issues and either want to make sure these programs can cure their issues or they don’t want to spend money on “necessary” programs:-
AVG
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ZoneAlarm
If you have Windows XP also keep all the security and critical updates installed every month, but using the Windows Update feature.
http://windowsupdate.microsoft.com
Once you have removed any malware from your computer then run a full CHKDSK (My Computer, Right Click on your C Drive, Properties, Tools, Check Now (tick both boxes, wil have to restart and let the tool run)) and DEFRAG (My Computer, Right Click on your C Drive, Properties, Tools, Defragment Now) on all your system hard drives.
I would also check out a different browser too:-
http://www.mozilla.com/en-US/firefox/
If you are going to buy a program then I recommend either Symantec Security Suite or my personal favourite is ZoneLabs ZoneAlarm Security Suite.