Thanks for all the replies.
I've taken the plunge and got the hosting company to add SQL server for this site. I've set up the SQL version of the forum on the server and everything works great with the empty database.
But... Now I am running into a problem in upsizing the old Access database.
Access is able to connect to the SQL Server database, and can see all the tables/modify what is in them.
But when I use the upsizing wizard it works away for a while then the report shows 'table was skipped or export failed' errors. Then for tblTopic it shows :
[Microsoft][ODBC SQL Server Driver][SQL Server]There are no primary or candidate keys in the referenced table 'tblForum' that match the referencing column list in the foreign key 'tblTopic_FK00'.
Trying to troubleshoot, I tried a smaller database from another site I run, again, I ran into the same problems using the upsize wizard. I was able to transfer the data from the smaller database simply through copying and pasting. This worked fine and everything was working. My problem with doing this for the larger database is that not all the records are sequential ( User acccounts have been deleted etc ) So if I copy and paste the data, the user id's in the SQL server database no longer match what was in the Access database.
Any suggestions would be very welcome!
Finally, In answer to some of the points above :
How many sites are on the server : Quite a lot, but most are fairly low traffic/low bandwidth. equestrianconnection.com is the busiest site on there with around 3000 uniques per day.
How Much Bandwidth for forum : Not sure, there's no bandwidth limit on the server so I haven't concerned myself with bandwidth usage up to now.
Bug with no Sig : Cheers for pointing that out, will fix that as I upgrade to SQL Server
Cheers!