You can have Umpteen Gigabytes of ram installed and any 32 bit OS can only see about 3 gig's of it.
So yes, if you can add just 2 gig's more, that would give you all that your OS can address.
But so few people are really RAM Experts, I advise going to the people who are.
You can just go to "www(dot)Crucial(dot)com and download and run their ram scanner.
It will scan you computer motherboard, to see what you have now and what you could add,
then it will take you back to the website, where they will display your current configuration
and recommend an upgrade for you. You will have several options presented to you, and if
you want to order your upgrade ram right there, you can, using your Credit Card.
They will mail your new ram right to your house.
I use them all the time for ram upgrades for my PC customers.
Crucial uses only the very TOP Quality ram (Micron) and it's fully guaranteed.
One gig of ram is barely enough (not really) for Windows XP, for Windows 7, not so much.
It WILL run, but very poorly.
Good Luck to you,