Up grading an olde pc

I have been given a pc that im fixing up for my farther. Its a Titan P4 motherboard with a 2.3gb athlon processor,windows xp home also with 512mb/ddr266 184pin 2.5 volt dimm of ram.

It has three slots for ram and the manual says it can support 3gb of dram (max)(ddr266/200)
It also says it supports ddr333/ddr266/ddr200

Q would i be best to install 1gb/ddr333 184pin dimm 2,5 volt x 2 and would this make a considerable difference to the life and use of my dad! sorry computer? Also are there any pitfalls with regard to ddr rams not bieng compatable. any help please im a novice.