I know Acer pretty well and I can't imagine them selling a laptop with such a small HD, only 1 gig of ram and Vista factory installed.
That one must have been a "Chef's Special".
To start with, M$ has given you most of the tools you need to keep a HD clean and running at peak performance.
Windows own "Disk Cleanup" would be a good place to start.
Running Defrag would be last after all garbage files and unneeded programs are deleted/uninstalled.
Then in the control panel, (Select Classic View) you'll find the "Programs & Features" applet. Double click it to run it.
It will give you a list of all the programs installed into Windows.
De'Install anything you don't want or need, by Right-Clicking on the filename and then clicking "Uninstall".
All trials and Demo's should get the axe.
Anything from 'Wild Tangent' also.....the axe. (it's Spyware)
If the little PC came with Norton or McAfee installed, it should be UN-Installed and replaced with a better AV program like AVG 8.0 FREE.
I do this stuff for a living and I find computers that are horribly loaded with junk.
Once they are cleaned and tuned up, they usually run 100% better.
Good Luck to you!
The Shadow