Use Of Wildcard In Cell Formula

I'm trying to use a "WildCard" in an Array Formula to both simplify and handle variations in several formulas.

My work sheet is used for Time Cards. I have a tab for each of the 52 weeks in the year and each tab is labeled "W1", "W2" for Week 1, Week 2, etc.

On my SUMMARY tab, I'm using an array formula that looks at cell "'SUMMARY'!D6" for a project number, and than searches through all of the Week Tabs for anyone that has charged time against that project.

The employee would enter the project number in D12:D35 of a given weeks tab with each row representing a different task for that week. In some cases they may have several rows for the same project number.

On the SUMMARY tab, the formula for Week 1 is in cell E6. For Week 2 it's in F6, etc.

I was thinking I could simply place the sheet tab name in the row above (i.e. D5, E5, F5, etc., and then write the formula for 1 cell and copy it to all of the other cells on that row.

Currently my formula looks like:
{=IF($D$6="","",SUM(IF('W1'!$D$12:$D35=$D6,('W1'!$N$12:$N$35))))}

I was thinking the formula might look like:
{=IF($D$6="","",SUM(IF('&E5&'!$D$12:$D35=$D6,('&E5&'!$N$12:$N$35))))}

But that isn't working.

Additionally I was hoping to do something similar on the SUMMARY tab by referencing a different spreadsheet with something like:
='[&A1&]Sheet1'!$B$51
Where cell A1 has the value "Time Sheets - 01-17-09.xls"Currently the formula looks like:
='[Time Sheets - 01-17-09.xls]Sheet1'!$B$51

But this isn't working either.