The user tonyem
posted a driver package for XP in the german amilo-forum:https://www.amilo-forum.de/topic,15413,-Vollstaendiges-XP-Treiberpaket-fuer-Amilo-Li-1705-da.html
FSC will not release any drivers for XP.
The Chipset of the Li 1705 supports at least 2GB of RAM. I'm not sure if the BIOS does but I'm optimistic.
Depending on your configuration you either need one additional 1GB module if you already have a 1GB module installed or you need two 1GB modules to replace the two existing 512MB modules.
A tool like Everest will tell you how many modules are in your notebook.
You need modules of the type:
SO-DIMM DDR2 PC2-4200 or PC2-5300