Get the right tools!
I second the recommendation for using a long bolt to hold the bottom bracket tool on tightly...there's just no way to do it by hand. If your spindle is hollow you can get a really long one and bolt it to the opposite end...if it's not hollow you'll obviously screw it in where the pedal would go. I bought a couple different length bolts so I'd be ready for different lenght spindles. Then I bought an extra big wrench that would fit the bottom bracket tool and a rubber mallet.
With the bike on the floor I held it in place against a shoulder and carefully whacked the end of the wrench with the mallet. Worked like a charm! And it gave me such a sense of satisfaction b/c the night before I struggled with that thing for an hour with no results.
Get the right tools! I think if you can unscrew the bottom bracket by hand (using a wrench of course) then it probably wasn't fitted tightly enough in the first place.