Why exactly does it seem low? The memory is storing all the files used by the OS, any applications running, any background apps, any data files, hard disk cache, drivers, lots of stuff. The OS also reserves a bit of memory, so it shows as "used" even though it's not. How much memory is available isn't an indication that you ONLY have that much memory available for any new programs to run in. The OS will get rid of unused files if it needs to free memory, or put data into the page file.
I have 512MB total memory, with 230MB available.