Well, TF isn't small/medium... but for comparison's sake..... TF uses over 100GB/mo and approximately 1GB of diskspace (not including logfiles). Expense is $160 for the vBulletin license, and about $120/month in server costs (we lease a dedicated server from rackshack.net - dedicated or colocation are the only viable options for sites of this size... well unless you personally own a hosting company hehe). The server also hosts Spoono and AbsoluteCross (each of which also use in the ballpark of 100GB/mo each). We can use up to the maximum capabilities of the server and up to 400GB of bandwidth per month for that price. Bandwidth does cost money.... any hosting company that says "unlimited" (bandwidth, space, etc) should be avoided like the plague.
Chances are, besides being very slow and unreliable... your cable company will catch on if you are hosting a server, and will call you and ask you to stop. Yours may be different, but I have heard that most cable companies disallow hosting servers on their networks. DSL is more likely to be ok with it though. Unless it's business-class DSL though, it is sure to bog down badly (and even the best DSL probably can't compete with the connectiveity of a real hosting company's data center).
Anyhow... some things to keep in mind 
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-- Dave
Neverside Admin
absolutecross.com
