help please! mysql tables become corrupt within minutes

Hi,

I'm desperately in need of some help here, I've been working on this with my hosting company for almost a month now with no success.

Setup:
Drupal 6.15
Centos 5.1 (4GB mem)
mysql 5.0.86
PHP 5.2.11 (cli) (built: Sep 21 2009 14:52:42)
Apache 2.2.3
Linux version 2.6.18-92.el5 (mockbuild@builder10.centos.org) (gcc version 4.1.2 20071124 (Red Hat 4.1.2-42))
Zend Engine v2.2.0

Basic problem is that drupal tables in the database (specifically cache, accesslog, watchdog, search_index) get corrupted almost as soon as I expose the site. By 'expose', I mean that the tables crash even while drupal is in off-line mode and barely any traffic is getting to the site - we have a robots.txt that has "User-agent: * Disallow: /" to help cut down on traffic. It happens within a few minutes of me taking down the external redirect.

Our host has just done an 'extended rebuild' of our mysql database to get rid of any lingering inconsistent data. This is of course after many imports from backups, repair table sessions on corrupted tables, a general troubleshooting.

Here is a list of the installed contributed modules, in case someone may know of an incompatibility:

addthis
advanced_help
calendar
captcha
cck
clickpath
content_access
ctools
date
dhtml_menu
emfield
feedapi
feedapi_mapper
feedapi_taxonomy_compare
filefield
flickr
icon
imageapi
imagecache
imagefield
imce
invisimail
menu_attributes
mollom
nat
node_import
panels
pathauto
plus1
spamspan
tagadelic
tagtool
taxonomy_role
tinymce
token
tweetmeme
viewreference
views
votingapi
webform
workflow

Sadly, I have no idea how to reproduce this error on other systems. I have attached a few screenshots of the mysql error messages from various corrupted tables, in case that helps. Any suggestions as to how to proceed would be most appreciated, I'm afraid my host doesn't know much about drupal, so they only really do what I tell them to do, and I'm now at my wit's end.

Many thanks in advance,

Ben Leduc-Mills