My forum is rather new, and i 've only 330 users on board.
I have Duron 700, 128MB SDRAM, 1xHDD (4GB - ATA 133) and simply graphic card and 10/100Mb card.
What part of my computer should I improve?

Is the forum the only thing it does? If so, then ram would be the obvious choice. Kicking that up with at least another 128 module or preferably higher. 500K of ram would be good on that box.

Is this hosted from your home?

Like ehill said, ram will definately help in this situation. But if you are hosting this from a home cable or DSL line, that too will cause the site to become slow with multiple users on.

I would suggest going with more than 500K. At least put in a nice SIMM of 1MB.

Sorry ehill. I couldn't resist!

No this is my own server but in proffesional company. I have 2Mb Polpack (DSL)

What you have to see though is how much throughput you get per day. How many concurrent users you have and if the max online is reached many times in a month/week/day. Also check your number of posts per day and analyze the logs to see how many page views you serve per day.

Some people here have circa 100 users online constantly so if you are not reaching those amounts think again about the upgrade. If those numbers are small you can forget the upgrade for the moment.

However, I concurr with the guys. Beef it up with RAM. In the future you can invest in a bit better processor but most importantly a SCSI hard drive to make it fly.

Warm regards

Nikos