The T110 only supports unbuffered/unregistered/UDIMM ECC memory.  It will not take RDIMM's (Registered ECC). Starting point: www.crucial.com/.../listparts.aspx I believe that the memory will be used across all slots to up 4GB for 32-bit, so 4x2GB (4GB usable) should give you the same performance as 4x1GB (4GB usable). However, I wouldn't hold your breath for an direct/in-place upgrade path from a 32-bit OS to 64-bit OS ... that will never be a possibility.  When you do eventually go to 64-bit (the 32-bit Windows server is dead), it will require a clean install, building the server from the ground up with/without file-based backups to restore.
We have a T110 running Win2K3 Server Std. x86, limiting us to just 4GB of RAM.  We currently have 2 2GB DDR3 DIMM's in the system.  Because of the nature of our software, we don't have a x64 upgrade path so we have to make due with the hardware we are given.  If I wanted to squeeze just a little more performance out of the system, would it make any sense to remove the current RAM and use 4 1GB sticks instead to utilize all available channels or would it make zero difference?  Alternatively, does the T110 officially or unofficially support anything faster than the DDR3 1066 speeds such as 1333 or 1600?  
T110 RAM Options for 32 bit system