Martin,
Not my area of expertise however would not a host be aware of DOS attacks.
Wikie, quite rightly says how it all can occur but not what preventative measures are available to the host.
Or doesn't the host care/able and leaves it up to you, the customer.
Do you know if we have our "own" dedicated server or do we share a server.
Get the impression that these 'attacks', for want of a word, seem to occur around the same time frame.
Also, it seems to be affecting the membership, in that, some members are not posting as often and some seem to be 'missing'.
Ah the joys of being in demand

and most popular kid on the block.