Just bought a 2Gig chip from the Vendors section for my Garmin 478. You must take an existing Garmin data card and use the case to house the new chip. So here's the quick how to pictorial.
First, remove the tiny Phillips screw from the back of the card.
Then, using a blade, pry the cover off the card. It's a pretty durable plastic and it will take a little persuasion at first.
Continue sliding the blade forward and the other corner will pop off. At this point you can continue removing the cover with just your fingers.
This is what it looks like open. At this point, remove the existing chip and replace with the 2Gig chip. Notice the black plastic locator pin in the extreme upper right corner of the board. This pin prevents you from installing the chip upside down.
Then, snap the cover back onto the rest of the case.
At this point, the front of my card bulged slightly.
I removed the cover and found that the back of the header bus on the chip is slightly longer than the original. I took a razor blade, pressed down and took about 1/32 off the plastic bus on both sides.
This is how much plastic gets removed
Reassemble the case, and replace the screw. I labeled mine with a sharpie.
ALL DONE, enjoy frosty beverage now.