It's the data files you want to be more concerned about than the software.
I would suggest installing a program such as "
eraser"
Then you delete all your data files and eraser will overwrite that hard disk space with jumbled data whcih makes any recovery very difficult.
Deletion of files, or even a simple reformat will not necessarily prevent recovery of data until the data has been overwritten by other stuff. That is why eraser type programs can work. They take their time though.
Now you can use the windows remove software functions. Or better still, reformat the PC and just re-install Vista, nothing else.
Of course to be really safe, install a different hard disk.