Sixty-four MB RAM is too small to run KDE or GNOME, the popular desktops. It's really too small to run Firefox or Thunderbird. It's too small to even load Openoffice.org. But you are in luck. Your motherboard can handle 768 MB (three modules) and the upgrade is pretty cheap.
I have a customer with a similar machine, 500 MHz Celeron with 256 MB RAM. Firefox, Abiword, and Thunderbird run okay on the KDE desktop. Openoffice takes 20 seconds to launch. The flash player is a little jerky but you can watch Youtube clips. To run those programs in 256 MB, you need a swap partition. With 768 swap is still nice, but you could get away without it.
So if you want to run something on it right now, try www.damnsmalllinux.org. If you want it to be a fun machine, buy some more RAM. I got a pair of 256 MB PC133 modules for $40 on ebay recently.
"I would like to use this pc as a backup and or test machine for running different distros."
That's a great idea. A test machine lets you mess around without breaking your work machine. And when your work machine's motherboard flakes out you can just stick your work drive in the test machine and keep going. There is one problem. The original power supply on that system is too small (135 watts) to support a second hard drive reliably. It's a funny little supply; the case is too small for a standard 300 W ATX PC power supply. But you can find a 200 W supply that will fit. If you just have one hard drive, blow the dust out of the case and supply every year and you'll be fine.
"Also I don,t have the bootdisc, would this be a problem?"
The boot disk that came with the computer would definitely be a problem. It's got a crappy operating system on it. If you find it, write "this stuff sucks" on it with a Sharpie and mail it to Redmond. Don't ever stick it in your computer.
I recently downloaded Ubuntu 6.10 on to a live cd and have been playing with it on my new pc and found that I like it.I was wondering if it would work on my old pc and what I would have to do to get it working. The pc is a old compaq presario 5000us.30 gig hardrive,74mb ramm and infected with viruses. Is this pc worth messing with? I would like to use this pc as a backup and or test machine for running differnt distros of linux. I would probably spring for some more ramm and possibly a hardrive.Also I don,t have the bootdisc, would this be a problem? Anybody have any ideas

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