HD Space varies each day??

[WildKat X]

Hey all, new commer here

I've got a quad core (q6600) w/ 3 gigs of ram dual 21" samsung moniters, 500 GB HD, and an x1650 se gpu

my question is this:

Usually every day I click on my computer (Vista) and it displays how much HD space is remaining. Every day is says between 145 and 149GB free. How can it vary so much, each day? Sometimes I will delete a program and gain 150B's free total, then use IE for the evening, play some Half Life Deathmatch, and then the next day, I'll be at 147GB's free. I honestly dont understand why and what is taking up THREE gigs?! I do regular scans, defrags and disk cleanup, so I have no idea whats going on..any ideas?

 

[WildKat X]

One thing just occured to me---could be the restore points that are taking up space, actually that might be it..

 

[Cromewell]

I'd say the most likely thing is the restore points or the page file. It could also be cached files for HL or something that doesn't get cleaned by disk cleanup.