so your saying all you have right now is a Laptop?
if so and your looking for a desktop i would just get something decent cause i dont think your the type who plays games on there PC which would mean you dont need a monster PC for your basic needs
typically speaking if you get a desktop i would get something at least dual core (from Intel since they have the fastest CPU's) and probably 2GB of ram. (2GB of ram if the PC u get comes with Vista... otherwise you could get by with 1GB on WindowsXP if your just doing rather basic PC stuff) and as far as hard drive space i think anything new (which will most likely be 250GB range or more) will most likely satisfy your needs unless you download alot of stuff.... but if you like keeping copys of dvd's you copy on your PC for a backup then getting a large hard drive will be a good idea and you can find 1TB (i.e. 1000GB, meaning about 212 standard 4.7GB DVD's could be stored on it ) hard drives for around the 100 dollar mark nowadays.
as far as DVD Burners... odds are no major mfg offers good ones so as soon as you get that replacing it might not be a bad idea. but not to worry since you can get a DVD Burner for dirt cheap on newegg.com (roughly 30 dollars out the door give or take a little, in fact u can get some in the low 20's out the door right now)
so i guess it just depends on what your going to do with the PC as to what you want to get , but i suspect what i said above is a good ball park figure.
but if you already have a desktop computer... depending on it's specs all you might need to get DVD burning capabilities is to buy a dvd burner online (i suggest newegg.com if your in the USA) for around 30 dollars.... which will most likely work unless your current desktop PC is ancient.
p.s. you said, "I trust the information I've received here in the past far more than that I'd get from an electronics store salesman." ... that about sums it up especially in the DVD Burner/Media dept cause you can pretty much bet money that vast majority of typical salesman dont have a clue about what's good and what's not etc etc.