I'm probably going to skip 8 and wait for 9... 8 doesn't really seem to have any advantages over 7 that are revelant to me, and it'll be quite a while before Windows 7 loses all support.
Especially since the rumor is that MS is prepping Windows 9 to be released only 2 years after Windows 8 in order to keep their business partners happy (since Windows 8 is basically a consumer OS no business would want to use). That's quite the quick turnaround.
The way I see it I would probably choose one of those two, because within 1-3 years the support for XP will stop if Microsoft hasn't change their mind which usually not happen to often. If you want to use ASP.Net or any network components then the professional is the right choice since they don't exist in Home Premium. However there is a couple of things that you should know that you can forget about Outlook Express since Microsoft has remove it from Windows7 and WinHlp32.exe is another thing you need to have a patch for, because WinHlp32.exe doesn't exist and you'll definitely need the patch if you're gonna be able to read the old help .chm files such as the help file for http://www.gamesas.com/topic/24-comprehensive-tutorial-and-useful-link-list/ (scroll down a little).
1. Why would you choose the retail version over the upgrade version just because in 2 years (precisely: April 8th 2014) XP support ends? That won't interfere with your upgraded Windows 7 copy.
2. ASP.NET is available on WIndows 7 Home Premium. I just checked
3. The only networking feature not in Home editions that is in the Professional edition is Domain Joining, which requires a Windows Server.
4. Outlook Express svcks and always has. Windows Live Mail replaced it in either case and other options exist such as Thunderbird. Though I think the amount of people using a desktop mail client isn't very high in either case.
5. CHM files work fine in Windows 7, you just have to set them as "Trusted" http://support.microsoft.com/kb/2021383
So it looks like the $159 version is the correct one for me
http://www.google.com/products/catalog?q=windows+7+professional+upgrade&hl=en&client=firefox-a&rls=org.mozilla:en-US:official&prmd=imvns&biw=1045&bih=531&um=1&ie=UTF-8&tbm=shop&cid=7510110190298611132&sa=X&ei=wx1PT4a1DMrlggfnxtXODQ&ved=0CH8Q8wIwAA
figures - oh, well, it's only money
Seeing as how that link just takes me to a listing on Google and at the top it says " pricing: OEM" I'll stress once again that you want the UPGRADE version, not the OEM version