is there a link that i can go to so that i can see which servers are suitable for use with asterisk and digium cards. e.g Compaq DL360, Asus RS Rackmounts, Dell 1850 etc…
any PC is suitable, with the exception of a few older Dell servers (and those only have problems with certain Digium cards, not * itself).
Any PC will do fine for running *, just as you can use any PC for running linux/apache (webserver) or linux/sendmail (mailserver) etc etc. Asterisk also doesn’t use much power- my PRODUCTION asterisk box (that handles all my business phone calls) is a P2-300. It has worked great for the last 2 years.
As for what you need it depends on your environment and your load. If you only handle 2-3 channels (simultaneous calls) then an old PC is okay for you as well as me. If you have 50 people on the phone at the same time, all going into PRIs then you want something better. Check the wiki page Asterisk Dimensioning for more info on that (wiki = voip-info.org)
And if you are setting up a datacenter you will maybe consider a rackmount box, or if its a high availibility thing with other things running on the box you may want scsi/hotswap/etc