A co-worker's car. He says he has to pump the pedal occasionally to get it to come up. Says it holds pressure once it does pump up. Where should I start? Haven't actually looked at it myself yet. If it's the m/c, are there any considerrations to take into account for the ABS?

Bleed the brakes first. Sounds like you have air in the system. If it is an ABS vehicle, cross bleed the system, right rear, left front, left rear and last right front.
Good Luck.

If you never opened the system it should not need bleeding unless the master cylinder ran low on fluid and sucked in air! Check your fluid level look for leaks i.e. master cylinder, rear wheel cylinders come to mind as being known leakers.