Under IPv4 I have been parsing the string representation of IP addresses to Int32 and storing them as INT in the SQL Server
IPv4
Int32
INT
SQL Server
If you are using SQL Server 2005, you can use the uniqueidentifier type. This type stores 16 bytes, which is perfect for an IPv6 ip address. You can convert between IPAddress and Guid by using the constructors and ToByteArray.
uniqueidentifier
IPAddress
Guid
ToByteArray