As many of you know that Vista is really not very good. Its very vulnerable for viruses and has had many security holes so far.
To make sure your vista is ok, we need to do somethings. As followings;

Have a very good antivirus like:
Kaspersky,
Eset,
Have a very good spyware killer like:
Spyware Doctor,
Stopzilla,
Ad-aware ,

And if you see any problem on your pc then do followings :
Start-start search-type;
cmd.exe and
type;
sfc /scannow

thats all!