It's important you find out what motherboard you have. The Duron 1.1 GHz should be Socket A, but it's not just a question of which socket.
Although there are still Socket A CPUs around (I think Semprons and some Athlon XPs), I suspect they will have a faster front side bus, which for a start your motherboard may not support. You will have to find out your motherboard model first.
Basically, if your mobo is MS-6340M version 1 or K7TM Pro, you can't upgrade to anything sensible. Funny thing is, according to the MSI website, these two motherboards don't actually support the Duron 1.1 GHz (don't know why not), which you have.
If your mobo is MS-6340M version 3 or 5, then you can get an Athlon XP, though the choice is still limited.
Do you have a motherboard manual from which you can find out the model number?