Since the holodeck is emulating living conditions, the computer itself would only be a part of the emulation process. Now if Data played ZSNES or something (hey, they could still be using that in a couple hundred years), then he's emulating an emulator on the emulated computer. Now if he's using WINE or something, then it gets a little more complicated. Data would be emulating an emulator on an emulated OS on an emulated computer. That's a whole lot of emulating...
>If Data was on the holodeck in a mock office setting would the
>pc be an emulator?
Consider that Data would probably continue to use the LCARS system that Federation uses in its computers if only because it was what he was most familiar with (we'll disregard the fact that Data's probably perfectly capable of figuring out another OS easily). Likewise, the holodeck computer would be less of an emulator than a terminal (much like the PADD systems you often see people walking about with). Of course, as Bgnome said, if the computer was using another OS that was totally seperate from the main computer core, it'd be emulated through the technology of the Holodeck. However, if the computer on the holodeck was accessing information contained within the ship's computers through some sort of conversion utliity (you know, Data was examining Spot's feeding schedules through Excel, despite entering the info on a PADD), the computer would be less of an emulator and more of a front end.