what I am looking for is a dedicated server with one celeron/p4 CPU to host one site, budget limits within $100-120/month, no DNS server/email server/control panel required, one IP is ok, what I will host is one forum writen in Java Servlet (Resin) with a backend sql DB(mySQL or PostGresql, prefer the latter), concurrent users are around 500 with 15 minutes, 300G bandwidth is ok. the following promotion (it's just $95) comes from Cyberwurx looks interesting.

350 gigs data transfer
2.4 GHZ
512 MB RAM
40 GB Hard Drive
8 IPS
Un-managed
Free Reboots
Redhat 9.0 or Choice of OS
FREE SETUP!

I am not sure if it meets my current requirements? I dont want my users to have lag. any idea is welcome. Thanks.

Umm don't even try it with a celeron.

Don't go with a Celeron, go with a P4, or a P4 with hyperthreading if possible. I'd also recommend boosting the RAM to 1GB if possible.

-Josh