I've also got a 1.1GHz T'bird, but I use it on an Asus A7N8X mobo. This mobo supports DDR RAM up to PC3200. I've got 1 gig of PC3200 installed and I have to run it at PC1600 (ie in sync with the processor, 100MHz) for the computer to run in a stable manner.
I did run the memory at it's rated speed (BY SPD in the bios) but this was giving me random reboots every day. I set the speed to AUTO in the BIOS and it is as stable as a rock and a [content edited] of a lot faster than it used to be with only 256meg in it! (I now get an average of 20fps on IL2:FB, whereas I used to get an average of 4!
Athlon XP 2500+ (stock) on an Asus A7N8X with 1Gig Crucial PC3200, 30GB Maxtor and 60GB Seagate Drives (both ATA100), Asus 9560 GeForce FX5600 graphics card, on board sound and dual booting with WinXP Pro and SuSe 9.2 Pro with a 400W Q-tec PSU. Using Firefox and Thunderbird for internet and emails and OpenOffice.org for work.