I have Windows XP installed and I have 3.4GB of physical memory recognized of the total 4GB installed because I have the large address memory configuration flag set in the OS.
Why are you asking if they have XP installed vs, Win7 when that really has nothing to do with it? I think you are probably confusing some people.
Win7 32-bit also only uses 2GB of memory just as XP 32-bit does. All 32-bit versions of Windows have that 2GB address space limitaion. So, migrating to Win7 will not help unless they migrate to Win7 64-bit and not Win7 32-bit. Technically speaking, Win XP 64-bit can also use more than 2GB of memory.
What you should be asking is for people to start using 64-bit Windows instead of 32-bit Windows. That said, it's not such a simple thing to ask and I'm surprised you'd do it. Most of the systems still using XP are old systems with less powerful processors with lesser amounts of memory to start with. First, at a minimum, you'd need to buy some more memory and you'd need to purchase a copy of Win7 64. Probably a few hundred dollers right there. Combine that with the fact that there's no way to upgrade XP to Win7 without installing completely from scratch (no upgrade install) and you have the reason most folks still haven't upgraded.
Due to the above issues, most folks just wait until they get a new PC to upgrade from XP to Win7, and rightly so. When they do get a new PC, they should make sure they get the 64 bit version of Windows 7, not the 32 bit version. I'm getting a new PC as soon as the Intel Ivy Bridge chips are out this spring and Win 7 64-bit is the version of the OS I'm getting for it. I'm sure many others will do the same as they are able to upgrade their PCs. It's just going to take some time. And you'll still have all those folks out there using Win7 32-bit. There's a lot of them.