The .NET framework is about 20MB if I remember correctly, and it is a big overhaul of some very low-level things. In a couple of years everyone will have it, but at the moment it is still quite experimental (even though MS have released it).
Win98 is just DOS with a GUI. WinXP is a proper OS, but bloated beyond reason. XP has the .NET framework already installed, but it is a *very* early version and should be upgraded through the WinXP Service Packs.
Both OS's have their nagative points, but if your PC can handle it XP is much more stable. I prefer Win2000 as it is nearly identical to XP, but less bloated.
I agree with col that we need a manager to handle multiple games. Maybe I will write one when I have finished some of my current games, it shouldn't be impossible.
There are standard dlls you can use to implement simple MAPI commands, or emails to you and me. I suspect that you need access to a public mailserver, and that may be the difficult thing. I am wary of this program that doesn't specify what outgoing internet email server it uses, as MAPI commands still need to use one...