i am happy to report that h.e.n work my N900 with the following:
1. a SSD(Intel X25-M 120GB 2.5") without using additional power supply. I got about 1.5hr of play time from playing mp3 off the SSD from full charge and speaker on.

2. a powered hub where it is connected to a Seagate 750GB 2.5" SATA drive and a cheap multi-format memory card reader(ie. CF, SDHC etc) at the same time; thus allowing transfers of content from the memory cards to the drive directly.

cheers

ps: both drives are in 2.5" h/d enclosure, with JMicron USB to ATA/ATAPI Bridge