Bicycle Mechanics - shifter compatibility?

Hello all. I am a newbie having not bought a bike in 15 yrs or so. I am ordering a Trek 7200 from a credit card rewards program as a starter bike. I don't know how cheesy that is but I want to find out whether I will enjoy riding, and in this case, can do so without spending a dime. I recently tore and had reconstructed my Right ACL as well as having most of the cartilage removed, so cycling seemed like an appealing fitness and recreational option. I will stick mainly to the roads as I don't know how well my knee will take to mountain biking. Any way, I haven't been to any bike shops, but I have been to a few of the big franchise retailers ( dick's, sports authority, etc). I was going to go for a Daimondback Maravista, being reasonably priced and smack in the middle of the market segment I was looking for (700c wheels, more upright position, front suspension). Again, don't know how popular this segment is, but the bike felt great. Then I found a similar Trek Bike that I could get free (well, nothing out of pocket). Few major differences that would cause me at this point in my cycling career to buy better components, but the one sticking point and issue I am having with the Trek 7200 is lack of trigger shifters (I like those over the twist type). So I'm hoping someone can answer this question:

Is there a compatible trigger shifter I can buy to replace the SRAM 3.0 Comp 8-speed that comes standard with a Trek 7200?

The 7200 drivetrain specs are as follows according to the trekbikes.com and the less I have to change or upgrade the better:

Drivetrain
Shifters SRAM 3.0 Comp, 8 speed
Front Derailleur Shimano C102
Rear Derailleur Shimano Alivio
Crank ShimanoTX71 48/38/28
Cassette SRAM PG830 11-32, 8 speed
Pedals Dual density platform

Thanks all, and I hope to have found a new obsession

Your bike choice should be just fine. Even low end Shimano/Sram components are completely functional(and better than the cheapest no name components that come on the low end dept store/WalMart bikes)
You didn't ask-specifically indicated otherwise actually-but live with the twist shifters for a while.I have found that they "grow" on you. They are simpler, more compact,and at least as durable as spring loaded trigger shifters.
If you decide to change them out, then you will have plenty of trigger choices. A rank guess is that any 8 speed Shimano trigger shifters will work since it has Shimano derails. Sram makes twist shifters with a 1/1 ratio for "its" derailleurs, but they also make shifters with a 2/1(or 1/2-can't keep it straight) ratio to work with Shimano derailleurs which are all 2/1.
This bike you are choosing is a good choice since it is a "name" brand, and it has name brand components.When you eventually sell it you will be able to trumpet the Sram/Shimano/Trek manu. and this will make the sale for you. The WalBikes and lowest end Dept store bikes have gone a couple of steps below the lowest end name brand components.The cheapest multispeed bikes now sell for $54+Tax which means they sell for $30 used. Your bike will never be a $30 bike.
All your components are just fine. The only thing you might want to change is the handlebars to get a more upright posture(if you are an oldster).You might decide to go for more or less aggressive tires(more or less heavily lugged depending on street or trail bias).
One way to judge how"good" a bike is is the weight,and the presence of Quick release wheels.Over 31 lbs for a bike with just front suspension is kinda heavy. Under 28 lbs for a "hardtail"(just ft suspension) is a decently light bike-maybe $400+ actual price as opposed to MSRPs which no one pays.Over 29.5 lbs for a no suspension bike is a bit heavy.
Don't spend a lot-$100's-on modifying this 1st bike. Get the hang og it, and them sell it and buy a "better one" if that is what you want.
The frame is what really separates "good bikes" from "functional" bikes-nice Chrome Moly steel-double butted(which means thinner in the middle than at the ends-makes it lighter,and gives the frame a more elastic feel with a softer ride), or the higher end aluminum frames are what you might aim for in the future.The bolt on parts are just "parts".
Sorry to run on.
Charlie