Using Excel 2002

I'm assigning session numbers to some classes in a general spreadsheet:

1A07
1B07
1C07
1D07

When type in 1E07 it automatically transforms it into:
1.00E+07

And I noticed that any time I use "E" it does this. I've tried to put
spaces in front but that doesn't make a difference.

Since I'm not a science whiz, can someone tell me what's going on and if I
can fix it?

Thank you!