Howdy, Len!
Welcome to the posting world. Don't let it intimidate you...if a stoner idiot like me can figure it out, you should have no problems.
First, you should be aware that the actual length of the videos you're posting will not strictly be relevant...it will be the size of the video file that determines whether or not you have to rar up a file. (I have 30 minute vids that are only 15Mb, because the quality sucks. 30 minutes of DVD quality can run well into the hundreds of MB.)
Most hosting sites have size restrictions on any one file they'll let you upload. For Rapidshare, my host of choice, that limit is 200MB. Meaning that if I have a 700MB movie to upload, I'm going to have to split/rar it into 3 sections of 200MB and one section of 100MB, and then post four separate files.
For you, this would mean the following:
Anything under 200MB would not need to be rar'd at all...you could just post the .avi or .wmv as-is.
Anything over 200MB, you're going to need to split up. If you do not already have Winrar, I'd suggest googling and downloading it. Once installed, simply right-click on the file you want to split, then look for the option "Add to archive." A box will come up: "Archive Name and Parameters." The name of the archive will read whatever the video name is, but you can change it in the text underneath the title bar.
At the bottom left of this box is a field that says "Split to Volume, bytes." Here, you can enter a number which tells it how large you want each chunk of the split. In the above example, I wanted 200MB chunks, so I would put "200,000,000" in that field. Hit "OK" and watch the magic happen!
The program will place the split parts of your movie in the same folder as the original, so now all you'd have to do is upload the parts, and post your links!
Have you picked a file host yet? Make sure you read the rules here about which ones are acceptable!
There are folks here who are very good with photoshop and screenshots, and could probably give you a fabulous visual tutorial on Winrar and posting. Tragically, I am not one of those folks, so I at least hope my ramblings were somewhat helpful. Good luck!