Are you saying CCleaner did not complete it's scan?
Per
http://www.bizrate.com/laptopcomputers/acer-aspire-5100-3949-2.0-ghz-amd-turion-64-laptop--pid653137864/, you have 1GB of RAM. Yes, experienced Vista users usually recommend 2GB for Vista. I've been using my Compaq Presario notebook PC with Vista Home Premium since July 2007, with 1GB of memory and find it runs OK for web surfing, email, and MS Office applications open simultaneously.
But, one thing you can do to improve performance with your current amount of memory is to review what software Acer installed that may be running in the background and consuming system resources. All the manufacturers install a lot of extra software on new systems that most users don't need and that can degrade performance.
But, again, no doubt about it, adding RAM would make a difference. 2GB of Kingston would cost $44. See
KAC-MEME/1G In addition to CCleaner, you might use
PC Decrapifier to help get rid of some unnecessary Acer stuff.
What protection programs (virus, spyware, firewall) are you using?