Gallery mysql optimization

[yacenty]

Hello guys, could You help me optimizing mysql server mainly for IPG?

Let's start from the begining.
Hardware:
Quad Xeon 2GHz,
8GB RAM
2 RAIDs: 3x146gb 15k rpm (RAID5) for system and website content, 2x146gb 15k rpm (RAID0) for DB and temp folder.

Web server: nginx
php: 5.2 with XCacher
mysql: 5.0

Board: 210k post, 8k users, over 60k pictures in the gallery and over 150k comments.

everything goes nice till there is 300users, after this board the server get stugling and runing very slow. After 500users online is reached the server is useless.
I hired technical admin expert to investigate what is the reall problem of my service. After one week investigation he told me - MYSQL is the biggest and worst serice for my server and it kills server.

Could You give me some hints how to modify mysql config and maybe mysql tables and indexes to get my site running nice even there is more than 500users online?
I think that hardware has big power and potential but it's not showing this performance.
What should I do?

Please IPB and IPG experts help me!!!
Thanks in advance,
BR

Jacek

[yacenty]

I had hired experienced server admin to investigate issue with my server is going slow.
He told me that first thing should be done to get it faster is to get away from IPG - I'm not very familiar with mysql queries but he told it's crazy strange how this queries take long time to be done.
He also told that there are not nice statment with rand() function used many time.

Hello guys could You help me a little bit with optimization?
Developers had You thought about rewriting gallery for the 3 version?

[yacenty]

according to bfarber's advice turned off random pictures - site is runing about 2 times faster :)
users can easily use it even there is 600users online