I have disabled all the services that i don't use (and I'm certain of what they do), using a guide in internet.
Now i remembered about the page file. It's the virtual memory. It says that it's recommended to use 6 GB, but it's set to 4. I'm not sure if I've changed it or it's by default like that

I have 4 GB of RAM, yes.
I don't mind that the free space is only 13 or 30 or 5 GB free space, as long as it works fine. I don't use that partition for anything else than the OS and the programs installed, and i have all the once i need there. I've got one HDD, devided in 2 partitions: the one with 50 GB for the windows and the programs, and one with the rest (about 180 GB) for all my stuff. My concern is if it needs this space, maybe it will run out of it sooner or later at it will need more.
The only big programs i have (and i use them often) are AutoCAD 2010 and Revit 2010. All the others are small programs, probably less than 50-100 MB each. I don't have any games. Ah, and the MS Office 2007 (word, exel, ppoint, project and visio). I'm not aware if the drawing programs make big temp files, but I don't think so. I will ask the IT manager in the university though.
So can you give me your opinion on how to set up properly my CCleaner - what to check and what not, and if there is something in the tools also?
Also what's your advice, guys? Should i change the location of the restore points and the page file to D:? Will it affect the computer's performance? As i said - I don't mind that they use the C: , as long as it doesn't run out of space.
PS: Is the defragmenting going to free up some space? I do it about once per month.