First you will need an always-on connection. It is suggest that you hunt around for a good bargin! Maybe look at www.pipex.net.
The line will need to be synchronous, ie. same upload speed as download. This will supply you with a static IP Address, in which your server can be located. In the UK you can pick up a 512k leased line for around £12000 ($18,000?) 64k for £6000 ($9000?).
To do this properly I would suggest buying a new computer to run RedHat Linux, it does not need to be too powerful. This will run web/mail/dns etc.. Having a seperate box will be more secure than running from your home PC! Place a firewall device between the server and your normal computer.
Then get the DNS from your domains pointing to your new server. That's it!!!
If you would like to discuss this in further detail email me, and I will be more than happy to help.