Dynamic formulas

Hi to all.
I want to know if there is any way to build dynamic formulas based on parameters...
example: =B1 & "sheet1!$A$2"

where cell B1 contains "C:\myxlsfiles\myfile.xls"

I wish to change B1 to B2 or any other cell with path or files values.

Thank you guys for your time.

=INDIRECT(B1&"sheet1!$A$@")

Let me know if that works

It doesnt work.
=INDIRECT(B5&"APE!$B$5")

or

=INDIRECT("'"&B5&"APE'!$B$5")

Sorry, my mistake...
Works only is the source workbook is opened. Thank you BigBas, a lot!

No problem. I'm glad you were able to solve your problem!