They will come with instructions if you buy a boxed drive. You can sometimes obtain an OEM drive that will come without the retail box and accessories for a $10-15 discount, but I wouldn't recommend that if this is your first time.
There is no mandatory software needed to run the drive. The controlling firmware is built into the drive and any version of windows will automatically use the appropriate low level drivers. Some drives will come with basic burning software, but if your main interest is burning DVD compatible video, you might be using 3rd party software anyway.
"Clear picture" is determined by the encoding software you use- the drive will either burn a legible copy (the majority of the time) or the data stream will break up and look like an over the air HDTV signal in bad weather.
Two hang-ups I can think of:
You will have to educate yourself a bit about jumper settings for IDE drives. Your new drive will likely be sharing an IDE cable with your old CD drive and you will have to make sure both are configured correctly. The jumpers are just small plastic coverings that can be manipulated with tweezers to cover the correct pins. Not a big deal, but something often overlooked.
When you decide on a drive model, you should choose quality media to get the best results. Different drives "prefer" different blank discs and more expensive is not necessarily better in this case. Taiyo Yuden and Verbatim discs are often considered good bets with almost any drive, while the "Great Quality" brand discs you see at Fry's are almost universally bad. If you do a little digging, the prices are often right there with bargain brands.