I just came across this Tetris game that is written in Flash for the PSP. I tried it out on my 770, and it's not too bad.

A listing of Flash games, including Tetris: Here

A direction link to the Tetris SWF file.: Here

Once the file is on one of the drives in your 770, open the Web browser and select the file.

Tapping the screen starts the game, and also pauses/unpauses. The rest of the game is controlled with the direction pad:

• Left and Right: Moves blocks from side to side.
• Down: Drops blocks faster.
• Up: Rotates the blocks.

The row dissipation animation a bit slow, but otherwise it's a nice looking simple Tetris experience... nothing like online, head-to-head Tetris on the Nintendo DS :-P