You'll be fine with that setup, given that the Wind River climate this time of year will likely bestow high temps in the 70s and 80s, nighttime lows in the 30s and 40s, and the occasional torrential thunderstorm. MSR's lightweight, tunnel-style Zoid 1.5 ($190; www.msrcorp.com) has lots of mesh, so will be a little bit cool during the night, although not intolerably so. You might even like the extra ventilation. But it has a full-coverage fly and sturdy design, so it will withstand wind and rain easily.
The kicker, though, is the Zoid 1.5 is only sold in Europe. Maybe two Americans were never meant to fit into a tent made for 1.5 campers, unlike those skinny Euros. However, MSR does sell the Microzoid ($180) for one person or Zoid 2 ($220) for two, both tents with similar features to the Zoid 1.5 and plenty adequate for the Wind River Range.
You also would do well with Marmot's EOS 2P ($269; www.marmot.com), a sub-four-pounder that still is freestanding (the Zoid requires stakes for support, although I can't say that gives me any heartburn), and has good ventilation and rain protection. REI's Sub Alpine UL ($219; www.rei.com), weighs a tad more, but is another solid two-person tent that's light and tough.
Be sure to pack a few extra stakes and a guyline so you can tie the tent down thoroughly, just in case a big T-storm vents straight down on you. I'd also recommend you buy some light polyurethane sheeting at a hardware store and cut yourself a light ground cloth to put under the tent. It needs to be slightly smaller than the area of the tent floor, as if it sticks out from under the tent it could trap rainwater.
You'll have a great trip. That's beautiful country.
Check out this year's more than 400 must-have gear items, including a comprehensive tents section, in the 2006 Buyer's Guide.