help please, new to OCing and dont want to ruin my card

hi all. i hope i put this is the correct forum since this is my first post.
anyway, i recently got an ATI X800XT PE AGP and its been running great, however, i did some research and found out that i could make it perform better. problem is i dont know how far i should try to push the thing, its standard speeds are the normal 520/560 and it idles on about 44c, under load is about 75, i got ATItool and used it to test its max core speed, the computer froze at almost 600mhz but the temperature didn't even go above 80c, i imagine this is because the card was running too fast and couldnt handle it or something. could anyone who has experience with this type of card reccomend core/memory speeds and fan speeds for each temperature please, its my first good graphics card and i dont want to ruin it, the PC crash scared me, i thought i had killed it. the card has been equipped with an Arctic Silencer 4 rev 2.

my PC specs are:
windows XP home
Pentium 4 3.06ghz
2GB RAM
ATI X800XT PE with AS4 (lol obviously )

thanks guys, much appreciated!
if any more info is needed, give me a shout