nunrleft - Your search didn't work, it might be better to explain how to use the "Search this Forum" link next time.
Since this is such a popular topic, someone should do an official write up that can be stickied, maybe for the "DIY Tech" section.
Some instructions from Fubarius
Help with pump spyder
joelrf600r's prettiest Spump I have ever seen
Custom Spyder pump.
Not so pretty but functional results, How to Make a Pump Blowback
How to Make a Pump Blowback - PbNation
SpyderMike's Stock Class Spyder
stock class spyder
Deus Machina's Pneumatic-Assist Spyder Pump
My first project, first post...
Some good instructions from PBN
Detailed STBB to pump convestion tutorial - PbNation