First, what version of Windows?
If W2K, or XP, I would increase RAM to 256MB.
It sounds like you have a memory leak.
These can be VERY difficult to track down.
Start by shutting down as many background programs as possible.
Close any program with an icon in the system tray that you do not use / need.
Use task manager (Alt-Ctrl-Del) to view other running programs. Again, disable any that you do not need.
How much free Hard Drive space do you have?
I like to have between 500MB and 1GB at a minimum.
Are you running a fixed size swap/paging file that is less then 500MB?
When windows runs out of real memory, it uses virtual memory.
When you use a fixed size swap file, you risk running out of virtual memory.
Check for Ad Ware.
Download and run AdAware from www.lavasoft.de
Bad registry keys can slow down a system.
Run a registry cleaner program such as Norton WinDoctor or V-Com Fix-It.
I usually find that I need to perform a CLEAN re-install of Windows to eliminate memory leaks.
This means backing up your data files, and formatting the hard drive.
Chas