I have been writing macros and utilizing userforms in Excel to use at work.
I am doing this on my personal computer and I am about 95% complete. I was
using pre-MS Office 2007. Work also utilizes pre-MS Office 2007. However, I
have upgraded both my personal computers to MS Office Enterprise 2007.

I am not using any complex macros. Basically, simple calculations, Date &
Time commands, and cell references (Range, Offset, etc). I did notice with
one of my personal workbooks that the NAME for the cell I used, "APR09", had
to be changed to "_APR09" (without quotes), in the 2007 edition of Office.

The two questions I have a
1) What do I need to do in order to ensure compatibility with the pre-2007
version
at work?
2) Why did the underscore have to be added to the cell name?

Thanks,
Les