I have a Mag 810 at home w/the same problem you do.
There's two ways to go with this one. On the one hand, Mag says that if your Dos text appears clear, but the Windows desktop appears fuzzy, it's because you don't have enough video memory. While I only have a 2 meg video card, I think this is a bogus excuse.
Mag also says that a certain amount of blurring around the edges of its monitors is "normal" as the tubes are designed to focus at the center of the screen. Yeah, right. Why do hundreds of other brands manage to produce crisp text and images on the edges of their screens?! Give me a break.
I've heard about this problem too many times to believe anything else than the reality that Mag monitors are pieces of s***. I picked mine up for $30 so I don't feel so bad. I hope you didn't pay too much for yours.
One thing I've found that helps is to keep my resolution to 800x640 and to keep the brightness down as low as possible. Even then, things get fuzzier the longer the monitor is on. I'm okay with it, as I just need a monitor to ocassionaly take a gander at my desktop and like I said... I only paid $30 for it.
How did you get your 810FD a monitor that goes for around 500 dollars for only 30 dollars? Or did you mean 300 dollars? I got mine about 4 months ago for 500 dollars, so this is an issue for me unfortunately.