Often the server load is high

[alamuae]

I am facing a problem with my forum that located in a very powerful server and the server contain only the vb forum.
the problem is the load of the server is often high it reaches (80%) some time although the specification of the server are quite enough to run it.

I have written this problem in the vbulletin.com
and this is the topic link:
http://www.vbulletin.com/forum/showthread.php?t=139532

after receiving a command from this Guy MarcoH64 the server load went down till 7 - 11% and I am looking for a better result and a final solution.

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About my database I would like to empty these four tables, if there is any critical problem if I empty them, please inform me or if it is normal send me the command that empty the tables without any errors.

pm 1,335,172 MyISAM 63.8 MB 47,022 Bytes
pmtext 526,413 MyISAM 306.3 MB 1,141 KB
postindex 69,701,315 MyISAM 1.5 GB -
word 2,232,375 MyISAM 167.7 MB -

I would like to reduce the number of the attachments for a specific forum not all forums, please give me the command that empty the attachments from one specific forum.

attachment 24,563 MyISAM 1.5 GB 55,384 Bytes