Unfortunately I couldn't locate that specific model number on HP's site. If you can't find the drivers on their site, that means that HP doesn't support Vista on it.
Does your system require drivers that are specific to HP? If not, then you should be able to install Vista. If you could find out what motherboard is installed and what video, LAN and audio drivers are required, it would be much easier to determine if all required drivers are available.
I checked a few SR1500 systems and they seem to have a RAM limit of 1 GB. That isn't ideal to run Vista and probably is the reason why HP don't support it.