how to make an envelope book

i look forward to reading the design sponge everyday and got excited when i saw this diy today. it's tax time and low and behold my hubby is an accountant! what a great way for anyone to keep track of all those little receipts and things, plus recycle old envelopes? i don't know about you guys, but this is one of those super, simple projects that you say to yourself "why didn't i think of that?".