What is computer set-up for on Mafia Wars?

The Computer Set-Up is used for other jobs.

More specifically, the Computer Setup is used at the Underboss level (levels 60-99) for the "Embezzle Funds Through a Phony Company" and "Take Over an Identity Theft Ring" jobs. You will ultimately need 263 of these to completely master the Underboss level.

The computer setup is one of three loot items that are dropped from the "Rob an Electronics Store" job at the Enforcer level. The other two items are an Untraceable Cell Phone and the Concealable Camera.

You will have to do the "Rob an Electronics Store" about 400 times to receive all of the loot items you will need at higher levels in the game. This will cost you a total of about 8800 energy (22 x 400), so just get ready to camp out at the Enforcer level doing the "Rob an Electronics Store" job for a while.

You also get these a loot drops during Fights. They can be found as secret stashes published by other players (found by them for doing jobs) and as part of Bonus loot stashes found during fights.