There's a demo floating about for the PC, iirc.
Also possibly a PS2 demo on the cover of a magazine.
Me, I just bought the game outright. I mean seriously, its just good fun. The manual is written for kids AND adults, from the point of view that its the KIDS who are letting the adults play, haha.
There's all sorts of neat touches too - one of the C3PO droids can have both arms and a leg sliced off. Grievous personal guard can be beheaded. You can kill Jar Jar and the larval form of Darth Vader. Killed enemies explode into their components. Also, you cant actually die, you explode but then just respawn.
There's not too much of a jump puzzle element - only if you want to find all the secret areas, but all the secrets can be unlocked by code if you're bored anyhow. I compared it to Jedi Power Battles.. for those of you who have played both console versions, it plays more like the Dreamcast version - no real jump puzzles, good level layout, camera not so annoying.
There are no voices, it mostly goes by expressions, and pretty much every single thing in the game is made up of Lego parts, from the starfighters to the big capital ships.
On an unrelated note, picked up Predator Concrete Jungle today... evil evil fun.