I upgraded my Vista laptop from 1GB ram to 2GB ram. The crucial.com system scanner tool says I now have 2GB installed ram, but in Control Panel-->System it says the ram is only 1,790MB. So why the discrepency of 210MB?
You probably have built in graphics. That uses up a part of your ram. It's probably 256meg rather than 210 that appears "missing".
If your pc can take a plug in card it will be quite a bit quicker with one properly installed.
If you ever decide to add one, remember to uninstall the driver and software before you fit the new one so as to avoid driver problems.