bit pf trouble with server resets

[exodus]

SMF Version: SMF 1.0.6
Hi,

Firstly the links:

hxxp:www.makenoiseanddance.co.uk/sx/ [nonactive] - The board itself.
hxxp:www.makenoiseanddance.co.uk/status.php?php [nonactive]

I've just begun using SMF, so I'm not familiar with it, but I've run other boards aswell, with no real trouble.  I'm having trouble with the site being apparently unable to cope with requests at certain times, but never times when anything particularly busy is going on.  Basically people get either a connectioon was reset error (firefox), or and general error page (IE) or a blank page(IE older versions); during certain times of day.

The box hosts several sites, but the logs show no real peak that would suggest that it's load is too high.  Some of the problems with access have occurred during daily backup, but many have occurred during random times, when the board is used a bit more, but even then only with the load at low levels.

Equally confusing is that the board does this when users are at peak levels, even though it often comfortably copes with these levels, I don't get many more than 15 at most times.