Problems sanding flat

I could really use some advice from those of you with machine/woodwork experience. I've always had a problem (a frustrating one at that) sanding to flat using my belt sander. It's a Rockwell 4" belt sander with 1/2 hp and I'm using something like 180-ish grit paper. I inevitably run into problems when trying to create a wedge, spacer, or sometimes just slimming down a piece of wood (for scales and the such). What happens: I always end up with an angled bit of wood. This is caused by, I guess, putting too much pressure on a particular part of the wood as I hold it against the sander. I'm very conscious of this problem though, and I try hard to distribute an equal force. I've also tried using a block of wood to hold the bit down against the sander, but invariably, I end up with two sides that are not parallel (or just plain flat). Making wedges is really tough; I don't feel as though I have any control over the taper that I'm putting on. Is there any trick(s) to sanding flat (or having control when tapering), or am I just horizontally challenged? Also, Is 4" too narrow of a sander to work with? Thanks for any help.
:banghead:

I use a 4x36 belt sander, the trick is to rotate and flip the blank often, none of the belts are even so you have to keep the piece moving to even out the irregularities in the belt...
Honestly I doubt the blank stays still on my sander longer then 10 seconds, before I rotate it end to end, or flip it over, rotate, flip, rotate and repeat :)

The wedge is very easy if you use a piece of double side tape to control the wedge, I just wrap a piece around my finger and have complete control of what I am doing.. The thin plastic carpet tape seems to work the best for me..

Belt sanders,like dremels can cause alot of damage (real quick)
Some things are best done by hand (block of wood and a pce of sandpaper)

Ain't that the truth! Any WECSOG graduates here besides me?

I haven't broken out my belt sander yet, but my plan is to use the belt sander to do the heavy grunt work, then bring the piece to a sanding block to finish the flattening with. I made a couple (100, 400, 600) out of 1'x4"x.75" pieces of maple. Used some rubber cement to glue the sandpaper (the 3M purple stuff) to the wood, giving a nice flat surface.