Try selling locally to save yourself the extra cost of shipping which goes against your overall profit. Keep in mind that most buyers will be concerned with warranty and that normally deducts $$ from what your system might be worth.
My guess is that $350-450 price range at your current config.
Yeah not having a warranty will be a deterent for some folks. Just the fact that it is used you should expect only to get 45-50% of the retail price. Me personally, I wouldn't give you anymore than $350.
Take some good pictures of the PC on, give a good description, make sure to say it's got a valid copy of Windows, and you can probably get around $500 on your local craigs list but don't be surprised when people offer you less. I don't know why you have 8GB of RAM with Win 7 32-bit, honestly.
if it had the 64 bit OS then you can sell it at around 500 bucks on craigslist. people will pay for it, of course those know about computer stuff will offer less. but im sure you can sell it for around 450-500 to a sucker somewhere.
i learned this trick at my old job. take off half the ram and put it on sale for 450 then offer the extra ram for an extra 50 bucks