What initial improvements can I make to a Schwinn Sidewinder? I bought a Schwinn Sidewinder from Walmart last night in a desperate attempt to get some exercise.  I took it home and rode intensely for an hour, it was fantastic!  I may be wrong, but I see bicycles as modular and upgradable and am hoping some of you might have thoughts on some initial upgrades that I could invest in (i.e. seating, tires).

I saw this question ( How can I get started riding without spending a fortune (too much)? ) and the very first comment was a bit disheartening "Wow! $500 is a cheap bike...".  I hate to say it, but where I come from, people might buy 5 bikes for $500!

Assuming I'll spend $50-$100 over the next year, what kind of upgrades can I consider?  Keep in mind I'm a penny-pincher, but very enthusiastic and wouldn't be adverse to finding parts at a Goodwill or other consignment shops.
$50 - $100 isn't going to get you much in parts, especially any that would be an "upgrade" from your current setup. If you're riding your bike often, it's possible that you'll spend an amount approaching that this year on new tubes and/or tires when you get a flat or wear your tires out.

My suggestion would be to ride this bike and enjoy it. You'll get your exercise and it'll give you time to research bikes and save for one that will fuel your desire for more advanced riding down the road when you gain your fitness. Visit some bike shops in your area and talk with the staff there to find a bike that is in your range of needs and budget. Test ride lots of bikes to find one that fits properly.

You don't need the "fastest" or most modern/expensive bike if you just want exercise. You just need something that is safe and functions for your needs. The best upgrade you can give your bike is the motor (yourself).