Interpoker doesn't have a no-download version, mostly it is the casino that use this. Poker rooms are not a major player in java, seeing as related sites can cross over skins. Take the Crypto sites for example, none of their poker rooms are java based. You will need to download the software.
However the difference with Interpoker is that you can deposit a min. of 20 units (£20/EU/$), party poker and such need you to make a min of 50 units. Also with Interpoker they have more tables, a wide variety if you'd like to call it that. The graphics and tables are simple yet advanced, you can fit 10 to a table, if you are looking for a tournament, I', taking it would not be a free roll and there will be a buy - in fee (is this the type you are referring to?), affiliates and the poker manager hold a right to free rolls but if you can provide what is needed, then bob's your uncle!
Also you have the choice to select if you want the tournie to be in EU/GBP's or USD's.