You will not get great speeds out of that computer as it is limited by the SATA 1 interface it will of course be better than an HDD but will top out on sustained read/writes at about 175-200MB/sec. For that resaon I would recommend you buy the cheapest SSD you can in the size you need you will not get the full benefits of any modern SSD so cheap is good.
The BX100 crucial series should work well and is a good bang for your buck but on an old computer like that you might consider a lightly used sata 2 SSD to save money.