ive just got an amd 64 3000+ processor with an abit av8 motherboard, and i need some advice on how to overclock it. ive tried using UGuru but it will only let me overclock slightly through the presets.
ive also tried going to bios and overclocking it there but every time the pc wont start up.
i have 512 mb of sdram, a friend said this could be an issue.

If you're not running 2 x 256MB RAM in dual channel mode, the RAM is the bottleneck in your system.

Also, you'd be better off overclocking via the BIOS

Asus A7N8X-X
1800+ @ 8 x 210MHz
512MB PC3200
Asus Ti4800SE 128MB
WinME/WinXP Pro

The Ram has to be DDR SD Ram or short DDR Ram because SD Ram wouldn't fit on that board.

With that board I guess you have a socket939 winchester core 3000+!

First of you have to set the PCI/AGP lock to 33/66MHz.
Next lower the HT multiplier (or HTT - name depends on bios) to 3x. With the socket939 board the HTT (FSB x HT multipl.) shouldn't run above 1000MHz and lowering the multiplier to 3x will keep you save at testing up to 300MHz FSB where I suggest to stop!
Then set the Ram to DDR266 (266MHz) and set the latency timings manually because otherwise the board might set faster CAS numbers automatically. The Ram clock will again rise at the same percentage as the FSB so with 300MHz FSB you'll be up at 400MHz Ram clock again (266MHz +50%).

Now you can raise the FSB. Go in small steps of 5MHz at first and 3MHz if you get to higher regions. Run benchmarks like 3DMark 03 and/or 05 to see if the system stays stable. If your graphic becomes unstable raise the VCore one step and try again (don't go above 1,6 or 1,65V and keep an eye on the temperature which shouldn't go above 60°C under 100% cpu usage).

I got my Athlon64 3000+ winchester up to 2700MHz on an Asus A8N-SLI Deluxe and before to 2565MHz on a MSI K8N Neo2 Platinum.

But if you do it that 100% your own risk and you loose your warranty on the cpu!

I wonder if a liquid cooled system could have bumped your 2700mhz up to 2800 or even 2900mhz.

Yeah you got to watch out because the main killer of a system is heat. I wouldn't even touch it unless you have some good cooling fans and some nice heatsinks. I'm iffy about stock stuff people say they can work, but I don't want a "can", I want a "will" and getting some nice cooling features will help you on your path to overclocking without fear of risking heat damage to your system.