You got a carrier pigeon in there?
My laptop is double that and I can go make a sandwich on startup.
I'd still back it up, but I think you should be able to refresh your OS without losing any info.
The best thing I ever did was get a network storage drive to keep all the pictures and music files on so they didn't take up space on the hard drive.
If you make the computer look for a needle in a bigger and bigger haystack, things tend to slow down.
How about a disk defrag? Have you tried that?