The loaded image's base address can be found in the PEB. You can get the PEB's base address by calling NtQueryInformationProcess with the PROCESS_BASIC_INFORMATION constant. The information you want is a 32-bit value stored at offset 8 from the PEB base address. There are plenty of examples of this in C, not too many in VB I can find for you. Have a look at:

http://www.vbstreets.ru/VB/Articles/66404.aspx

You'll want to follow the same technique, calling NtQueryInformationProcess to get the PEB base, then use ReadProcessMemory to read 4 bytes from PBI.PebBaseAddress + 8 and that's your base address to read the process image from virtual memory.