Assuming that you don't have a hard coded IP address from your ISP (which makes it easy with the IIS server in the WHS) you can sign up for a free subdomain name administered by Microsoft's Windows Live Custom Domains service via the homeserver.com site which will take the form of "mydomain.homeserver.com". This does require a windows live id, but it is a dynamic DNS service so even if your router's IP address changes, your subdomain will be updated to point to the new address. (Windows Home Server periodically polls the router for its current IP address and sends that address to the dynamic DNS server on homeserver.com. The server then updates its DNS database with the current IP address of your router.) and Walha....you can get there from anywhere.
You could also use a pay for Dynamic DNS service but why pay for what is freely provided with your WHS.
For detailed how to information related to WHS I highly recommend the book "Microsoft Windows Home Server Unleashed". Great book.