It looks like your computer has 2 slots for memory, each holding a max capacity of 1GB. If you want to upgrade to 1GB, you need to find 333- or 400MHz DDR memory:
Documentation
The slots are comparable to video card slots in the sense that you slide something into them, but they (obviously) have different features.
Coming from the states, you can buy 2x512MB RAM for $40 including shipping:
Newegg.com - 1GB (2 x 512MB), 184-Pin DDR SDRAM, Desktop Memory, Memory, Computer Hardware