WordPress MU

We have a new website, having recreated from scratch in WordPress MU after using ASP.net for 5 years.
I'm getting numerous complaints from subscribers that the site is slow to load so I ran some tests in 3 browsers [IE8, Chrome 2 & Firefox 3.5] Time to load home page in seconds [adventuresportnq.info] was 28,15,21.
Any ideas as to why it's so slow in IE and what I can do to fix it?

Have you done any tuning? MySQL might need some tweaking and are you running anything like wp-super-cache or php level accelerators?

If you;re adding a lot of crap to the head via plugins, that'll do it too.

Andrea_r - We've deactivated all plugins except: Akismet, Exclude pages from Navigation, Exec-php, Formbuilder, Google XML sitemaps, Headspace2, mailfrom, widgit logic, random image widgit, wordpress.com stats, wp table reloaded & wordpress database backup.
Do you know if any of those are particularly resource hungry or cause problems?

SteveAtty - Pretend I'm new to this [which I am] and point me to how I might 'Tweak' mysql and what will that achieve?
I have wp-super-cache loaded but deactivated at present - could it help if it was activated?

Thanks guys for your assistance, I hope there is something I can do to fix this problem as I'm getting plenty of complaints.
cheers
emmsee

You have 3 files that aren't loading (returning 500 server errors):
prototype.js and two attempts to load jquery.

You are then loading jquery.min from code.jquery.com for some reason, which is slowing down your site considerably.

I would switch to using the google ajax libraries instead, which could speed things up quite a bit.