8:26 p.m. on January 4, 2005 (EST)
Josh -
First, no tent is perfect or even suitable for all seasons or all climates (No such thing as a "tent for all reasons" or all seasons, for that matter). You will have to compromise or make do if you insist on having only one tent in your portfolio (you don't have to do like me and acquire a dozen tents, though).
I am not a fan of convertible tents for use in winter snow camping. The main reason is that any open mesh, even covered by a zip-in/out panel, seems to let spindrift in, at the very least, and some of them let more substantial flakes in. Also, convertible tents tend to be significantly heavier for the space than a dedicated 4-season tent.
That said, a lot of 3-season tents, especially if they do not have open mesh, work very well for mild winter/snow conditions. I have even used my old Sierra Designs Sleeve Flashlight in fairly serious winter conditions, despite the fact that the front door and tiny back window of the main tent body are mesh. I don't dare use my newer Clip Flashlight this way, though, because it has mesh panels on the sides as well.
I also have a Sierra Designs Meteor Light that seems to work (so far), despite having a fair amount of mesh.
Frankly, though, I do not understand the current fad of making the main tent body of even a 3-season tent mostly mesh. Yes, I know, it provides lots of ventilation (except that putting a decent fly on it that actually keeps out rain greater than a light drizzle in no-wind conditions defeats the ventilation, and even then a good breeze can whip the rain under the fly and through the mesh with anything less than a full-coverage fly). And supposedly on clear nights, you can leave the fly off and enjoy the stars - except that the mesh strongly interferes with a clear view of the sky.
The main thing in sleeping in cold weather is keeping the wind off, plus sheltering you from any precipitation. One thing that can happen with a largely-mesh tent in cold weather is that your body moisture will condense on the underside of the fly and drip through the mesh onto you and your sleeping bag (or freeze and the ice crystals will snow on you when you brush the tent sides). You can easily make up for the colder nights by increasing the warmth of your sleeping bag (a warmer bag, a liner, a blanket inside or over the bag, heavier long johns, that sort of thing).
As far as holding the snow, the basic rule of thumb is "the number of poles equals the number of seasons." So a 3-season tent needs 3 poles and a 4-season tent needs 4 poles. Yeah, Jim S and I use our Bibler Eldorados in the winter (heavy storms, at that) and they have only 2 poles. There are exceptions, but you pay the price.
If you were considering serious snow camping, I would recommend looking at a tent with 1 more person capacity than you intend having in it. 2 people cooped up in a storm in a 2-person tent gets pretty claustrophobic, but a 3-person tent is more livable. For your "a little snow", a 2-person tent for 2 people is fine. A usable vestibule makes things somewhat more livable. But adding room inside or in a vestibule adds weight. Again, if you were considering serious snow camping, I would suggest having 2 real doors. But "little snow" says a fairly cozy tent with a single door will do just fine (check how cozy you and your companions can stand, though - I once had to spend 2 nights in a 3-man expedition tent with 6 of us in it - got pretty tight after a few hours).
So, I would suggest that you consider a tent in which the main body is regular ripstop (non-mesh), and the door is mesh with a zip-panel that stays attached. It should have 3 sliders so you can vent the top and bottom of the door to promote ventilation (and reduce condensation) while still shielding against drip, frost-snow, and blown-in spindrift. I also suggest the "solid" door panel should be on the inside and mesh on the outside so in mosquito season you can open the solid panel leaving the mesh zipped up from inside the tent (keep them varmints out!!) The fly should be full coverage, coming to within 3 or 4 inches of the ground all around (allows some ventilation while reducing wind-blown precip).
Take a look at expedition tents (in person, not just catalog or web pictures) and think about the way things are arranged and why. Then carry this over to your 3+ season tent requirements (example is no exposed mesh, no zipout panels to lose).