ok, sounds to me first of all that whoever sold you the PC sold it as 'Vista Ready'. in other words it can run the basics of vista with all the features turned off. hint for the future, dont go to PCWorld as they sell entry level stuff for performance prices.
now, back onto the problem. you should not listen to people when it comes to your OS performance. These programs are commonly filled with rubbish and maybe some other harmful stuff like keyloggers and malware.
onto fixing some problems. first download and install windows defender. this will get some of the most common malware and will also find some problems with your PC.
http://www.microsoft.com/windows/products/winf amily/defender/default.mspx
next, get yourself AVG. this is one of the better anti-virus programs which you can get for free. although i would suggest that you find a better alternative such as Kaspersky or ESET smart security.
http://www.avg.com/filedir/inst/avg_free_stf_e n_85_336a1515.exe
run AVG to scan your PC for other viruses.
one more thing as well. if you have turned off windows updates then i strongly suggest you perform one before you do all this.