using the router you'd make four passes - one for each "corner" of rectangular stock, rotating the stock as you make each pass.
you would need to invert the router in a table top (so that the bit points up through the table) for example:
http://www.leevalley.com/wood/page.a...,43053&p=43885
a router will cost around $160, a table setup around $300 and the cutters/bits another $100 or so.
plus the cost of the wood, which is suprisingly expensive especially if you don't have the equipment to convert rought sawn lumber into usuable boards.
plus the finishing supplies, and if you don't have spray finishing equipment, the finishing alone would take a very long time.
now, if you want to do it the old fashioned way all you need is a spokeshave, wood, and a whole lot of elbow grease:
http://www.leevalley.com/wood/page.a...t=1,50230&ap=1
(of course you'd still have the finishing to worry about)
fwiw, i've got quite a bit of woodworking experience and i own the necessary tools, but i still wouldn't try to make my own window blinds.