first, what i am about to say is my personal opinion. i have never had any problems changing the oil in this way, but "my way" kinda scares most people away.
not a dumb question at all, lots of people get confused. basically yes, the 98 and 05 sportsman are going to have the same procedure. with the 4-stroke it is really not neccessary to prime the oil pump like you would want to on a 2 stroke. just like the guys at the quick lube dont prime your oil pump on your 4-stroke car.
now, so we have a dry sump system on both machines. when you pull the plug out of the reservoir tank, you will get most, but not all of the oil. there still will be a small bit of oil in the crankcase. there are drain bolts on the right side of the machine that drain that last of the oil out of the crank, but they are a pain in the ass to get to. what i do, and this is the part that freaks people out, is after letting the reservoir tank drain, i turn the machine on, with the plug still out. as the machine cranks over and starts up, the oil pump pushes that last bit of oil in the crankcase out through the reservoir tank. when the machine is running, you watch the oil plug. oil with start pouring out as soon as the engine starts to crank and fires up. THE ENGINE RUNS FOR ONLY ABOUT 7-10 SECONDS. as soon as the oil starts to turn into a dribble, you shut the machine back off. now all the oil is out. just change your oil filter, put the plug back in, and fill her back up.
now, i have had a discussion with mechanics about this. this process was actually explained to me by a mechanic. and if you think about it, running the machine with almost no engine oil in it for a few seconds is no worse then when you first start up your machine with no oil pressure. either way it takes 10-15 seconds to build oil pressure up after you start, and changing the oil this way the engine runs for even less time then that.
now with that said, you can do serious damage to your engine, so be careful. but its pretty clear when to shut the machine off if you go this route.