Info from Barry Canton (MIT):
The T7 promoter has a low background if you can keep the expression of T7 RNAP relatively low, in which case it will be rare that it will find its promoter. So you need a promoter that you can turn relatively off, hook that up to T7 RNAP and then use a T7 promoter to control the gene you want to have tightly off.
Warning: T7 RNAP is highly active so if you make a lot of it, your cells are likely to stop growing assuming there is a T7 promoter for the RNAP to bind to.
The two key papers on using T7 RNA polymerase and promoter for the expression of cloned genes are attached.
There are E. coli strains that have T7 RNAP integrated into the chromosome (BL21(DE3)). Novagen sell plasmids that have T7 promoters in them.
The relevant BioBricks are -
I2032 - sequence verified by me, not yet tested. R0085 - consensus T7 promoter sequence. Tested by me and working.
Hope this gets you started,