I need to replace the ram. One of the ram is bad. What's the best option?

at the HP website, look up what type and size of ram that machine can handle.

and then i'd buy the maximum amount it can handle and install it. or else, junk the machine entirely -- it's WAAYY old.

its so old is it worth the bother? the max you can fit is 4 x 1gb they probably cost about tuppence and would make a difference to your low 2gb fitted at the moment even replacing two with 2x1gb would be better than you have now. most current AV's have a critical performance change below 2gb(they go terribly slow). as for any thing else well you dont have many options.

That would depend on the computer, not the specs. Usually the spec sheet would include the amount of RAM it could take & how much & which kind.

To replace the RAM may cost more than that antique is worth. Hint: don't spend more than 5 bucks for the RAM.

I'd look around on ebay for some second hand "240 pin, DDR2 SDRAM" that's what that computer takes DDR2. Speed doesn't really matter, It can support up to 4GB over 4 dimm slots.