HD1 is kinda a stupid investment. Just about any good quad core will have more processing power, will cost you way less in plug-ins, and with the right interfaces you can get just as low of latency. The only real way to get into HD is if you can spring for an hd2 system (at least). Trust me, work on a HD 1 and try to run a full 30-40 track mix with normal plug-in instances, its not going to be fun. There is not enough processing power.
HD is a great system, ( I personally dislike working in PT but...) its just not practical to get an HD1 system to try to make money off of. I'd wait until you can get into HD2 or see what comes out of avid in the near future. Ya never know...