Vocals/Lead Guitar - Beatrice (the Umineko series)
Rhythm Guitar - Eleanor Lamb (Bioshock 2)
Bass Guitar - Chell (Portal 2, when she actually looks attractive with the improved graphics)
Drums - Paine (Final Fantasy X-2)
Keyboard - Rikku (Final Fantasy X - different game, technically, so still counts! HAH!)
And if we can choose who does things like the sound and lighting and such, I'd have April Ryan (The Longest Journey) on stage design and as manager and whatnot. She's an art student, after all, so she'd be good with that. Also, it fits with my aim at making the band full of young attractive females. Hey, it's a band, I want it to be popular for the charts - and sex sells, right?
If I could choose any fictional character rather than just gaming characters, by the way, I'd have Hannelore from QC on drums. Again, fits the aim and theme, and she actually plays drums in QC, so yeah...