The 100 Credits is to unlock a game for Free Play mode. Free Play mode lets you play a table as many times as you want without spending any (additional) credits.
Tables can also be unlocked for Free Play by completing all five goals for any table.
Jive Time is the only table in the 360 version that needs to be unlocked before playing.
Unlocking it requires completing the Williams Challenge from the main menu. This challenge involves beating set high scores on the other 12 tables in one sitting. The order is as follows:
- Gorgar - 100,000
- Taxi - 1,000,000
- Pinbot - 600,000
- Funhouse - 2,500,000
- Black Knight - 800,000
- Space Shuttle - 1,000,000
- Firepower - 200,000
- Whirlwind - 2,000,000
- Sorcerer - 500,000
- Tales Of The Arabian Nights - 3,000,000
- Medieval Madness - 15,000,000
- No Good Gofers - 8,000,000
Some of these scores can be difficult to get consistently if you don't know the tables well, so it might be best to try completing the other tables' Basic Goals and unlocking Free Play on all of them before attempting the challenge.