lets start with the basics
right click my computer then select properties
bottom left select performance
then top left open disk cleanup
then click ok
in the resulting box click the more options tab
under system restore and shadow copies select cleanup then delete then ok
this will delete all but your last restore point so make sure your happy with that first
see if it gives yuo any extra disk space
NEXT
Vista stores files from service pack updates and routine updates so you can uninstall them at a later date , however these can sometimes take up gb's of space and can be deleted , but remember if you do delete them you cannot uninstall any service packs
this will tell yuo how to delete the old SP2 files
http://www.vistax64.com/tutorials/229239-sp2-disk-cleanup-tool.html?ltr=S
oh and if you use the windows search tool it'll find appdata for you

though it really shouldnt be that big .... you probably cant find it because its hidden , if you goto folder options in control panel then VIEW you can select it under "hidden files and folders"