What motherboard do you have? It will all depend on the socket, the 9550 has an AM2+ socket whilst the X6 is probably running on AM3 socket. If the motherboard doesn't support AM3 CPU's, it may not work.
If the motherboard supports AM3 CPU's, make sure that it can handle the 125W CPU's as well. Because the 1090T is highly overclockable, it will require more power to run. Ensure the motherboard supports up to 125W CPU's before you buy.
EDIT: I just noticed the 1090T is backwards compatible with AM2+ and AM2, so the socket support is no longer an issue. Sorry, I'm not the best with AMD...
The list of compatilbles are all AM2 or AM2+ and I've looked for those, I know this is an old computer im not looking for the best CPU just something about a 2.8 or so. Im not sure where to tell if it will hold a 125w cpu so heres what is says
Micro-Atx: 24.4cm (9.6 in) x 24.4cm (9.6 in)
NVIDIA GeForce 9100
Front-side bus speed
Socket Type: AM3
n im not gonna list the rest but here is website if im missing nething
Following that linky I've come to the conclusion that that motherboard will support a 125W TDP CPU (I think it supports up to 140W, if I'm not mistaken). That means the 1090T will fit, and you can go for it if you have the $$.