There is no getting around the lack of trim command with windows XP, however, the Samsung and intel SSDs still perform reasonably well (And to a certain exetnt one of the OCZs, vertex IIRK) .TRIM would improve them though. Also leaving space on the disk does not help very much, as all SSDs perform wear leveling, to avoid over stressing one block of flash. This means that your swap file alone will quickly mean that all of the blocks have been written to at least once.
Do not use a defragmenter on an SSD under any cirumstances. Firstly it's not needed as all parts of the 'disk' perform equally, but the main reason is that it will significantly reduce the SSDs lifespan.
With the wear leveling, I believe you need an OS that is aware of this, and I'm not sure if XP is, windows 2000 certainly isn't. Vista and win7 do understand wear leveling IIRK.