I'd say you're still making a mistake, and not just on the mixup on KB vs. MB.
It is not a very difficult thing to install RAM. The hardest part will probably be trying to get your hand around in the cramped HP case.
Of course, for a non-gamer, 512MB should be plenty. If you're experiencing poor performance, have you investigated the possibility of a spyware infestation? I won't repeat the basic instructions on how to check and deal with this problem, since it's been covered probably hundreds of times on these forums. So, feel free to search these forums, or even a search engine such as google.
I will, however, offer up my collection of dos and don'ts for keeping a well running system. Something I've posted many times, but have saved at the ready to be inserted into posts with only a few clicks of the mouse. Yes, sadly, I do need it that often.
TIPS FOR A SMOOTH RUNNING SYSTEM
The more of these suggestions you follow, the fewer problems you should have. Follow them all, and you've probably eliminated at least 95% of all potential problem sources.
Things you should NOT do
1: Use Internet Explorer
2: Use any browser based on Internet Explorer
3: Use Outlook or Outlook Express
4: Open email attachments you haven't manually scanned with your virus scanner
5: Open email attachments you were not expecting, no matter who they appear to be from
6: Respond to spam messages, including using unsubscribe links
7: Visit questionable websites (e.g. porn, warez, hacking)
8: Poke unnecessary holes in your firewall by clicking "Allow" every time some program requests access to the Internet
9: Click directly on links in email messages
10: Use file sharing or P2P programs
11: Use pirated programs
Things you SHOULD do
1: Use a non-IE or IE based browser
2: Always have an up to date virus scanner running
3: Always have a firewall running
4: Install all the latest security updates (the exception to the no-IE rule)
5: Delete all unsolicited emails containing attachments without reading
6: Manually scan all email attachments with your virus scanner, regardless of whether it's supposed to be done automatically
7: Copy and paste URLs from email messages into your web browser
8: Inspect links copied and pasted into your web browser to ensure they don't seem to contain a second/different address