Aikeedoh, I'm not understanding something about your description. There are two ways the value of a cell is displayed in Excel. (Actually, someone else may chime in here and tell me there are more than two, but I can think of two just now). The ordinary way is in the cell itself; you use formatting strings to control that. And the other is what you see in the formula bar at the top when you select the cell.

Now, you say the data "looks like this 100:03:00", and I suppose you mean in the cell. And you say you want it "to be shown as 100:03:00", and again I suppose you mean in the cell. So if you want it to look the way it already looks, what's the problem? And yes, when I type 100:03:00 in a cell, it shows up as 1900-01-04 04:03:00 in my formula bar; that's normal.

Second, you're worried about how it will work with VLOOKUP. But unless I've misunderstood you, that isn't a problem; how it's formatted won't affect Excel's ability to find it with one of the lookup functions. You could display it as "100:03:00", "4.16875", "4.169E+00", "4 27/160" or anything else you can think of and Excel will still find it correctly with VLOOKUP.