I had second row tickets to Dave and Tim in 2003 and this is the way Dave played Let You Down:

e|-------------------------------|
B|--8----7-----------------------|
G|--x----x----6----7----7--------|
D|--5----7----x----5----4--------|
A|--7----5----7----x----x--------|
E|------------5----7----7--------|

The strumming pattern isn't too bad and he just plays this progression for almost the 
song. Towards the end, however, he plays a slightly different progression which i think is this:

e|---------------------------------------|
B|--8----3----5--------------------------|
G|--x----x----x----6----7----7-----------|
D|--5----4----5----x----5----4-----------|
A|--7----2----3----7----x----x-----------|
E|-----------------5----7----7-----------|

Booyah.