Yeah, definitely try out any "Lite" version of desktop app before buying. There is a wide range of performance. Some work better for data entry (like you want), some do better at streaming video/audio (but are worse for typing / mousing around).
Also, since your Windows 7 is running under VMWare, you need to make sure VMWare networking is configured properly. Basically you want to setup Windows 7 to share your network, and request an IP address from your router's DHCP. That way, your iPad will be able to directly connect to the Windows 7 VM. By default I think VMWare does a private network that only allows access from the host. (I'd give you a step by step, but I use Parallels for my VMs).
I know a lot of folks who do the same type of thing you're talking about. Once you find a good desktop sharing app, and work out the networking, you'll be good to go.
