SSD on an old mobo that is sata1 or 2 and does not suppor AHCI will not help much. You will get some speed benifets as long as the SSD is mostly empty. But as it gets full and is used more it will slow down. Eventually the SSD will be slower than the mechanical drive.
The mother board really has to support AHCI (advanced host control interface) in order to make a SSD feasible. With out AHCI the computer will not pass the trim command down to the SSD so it wont delete old data when you delete. Instead the old data will be deleted when you need to write over it, causing a very long write delay.
Windows XP isn't very SSD friendly and XP is unfortunately not supported TRIM. The TRIM command enables the OS to notify the SSD that old data is no longer valid. TRIM is non-specific to either SATA controller mode, and will work equally well in both IDE and AHCI-mode.
Just over-provision the drive and you should be fine since you don't have TRIM. This is the best thing you can do if you don't have TRIM. Depending on how much you over-provision the drive, your speed should hold up just fine. I say over-provision at least 20% of your capacity.