The problem you described is totally normal, it is like mciahel said. The power consumption of your 250GB drive is too large. I’d assume during the spinum the current is larger than 1A. There are USB Y-adapter cables available, than the drive might work, but I’m not a fan of this y-adapters.
I’d recommend using an external power supply with your drive. With expternal power there should not be any problem.
BTW, there is no 2.5" on the market that reaches the USB specification for buspowered devices. Even 80GB or 40GB need too much power. Some older Toshiba HDDs (40GB, 4200rpm) reached the 500mA. but this drives are not available anymore since 3 years or more… No drive with a spin rate of 5400rpm or faster would reach the USB specification. Maybe a 4200rpm drive would come close, but I guess not close enough…
If you would like to have a drive working buspowered I’d recommend a 1.8" drive. I have a 1.8" USB powered drive (60GB, 4200rpm) and this works fine sinse this special HDD also works with 3.3V as voltage. I never had problems with spin up.