Is there a way that I can use data from a cell to reference a worksheet?

I have two columns with data in.

The first column (called columnA) contains values which match the names of
my worksheet tabs. The second column (columnB) contains references to items
found in those tabs.

I want to be able to use the first colum to speciy which tab to look in and
the secound column to be able to use the VLOOKUP function to then grab data
relevant to that entry. I can do the second bit but the first is proving
very difficult.

I need to somehow use the data contained in a cell to reference a worksheet
tab?!