As a thief? Hmm - I will have to check that myself - that would be a lot of hp for anyone! (They are already unfair enough in that they get HD after 2nd level of bard (regardless of their previous HD.) This would give them a maximum of 7d10 + 9d6 + 10d6 + 12 hp... or 196 hp! (To get the equivalent (sans CON bonuses), a fighter would have to reach level 44 or so, requiring about 9,000,000 XP. The maxed-out bard would only have accrued about 3,174,000 XP, on the other hand... The only detriment of the bard would be that his THAC0 is only that of a 7th level fighter, but he does have most thief abilities, up to 5th-level druid spells, and other powers, so I would say that bards have the edge here
)
...but anyway, I would (as a DM) not give bard-wannabes the thief HD (anyway, the bard-wannabe might change his mind and stay as a dual-classed fighter/thief).