Gave it another shot and managed to get VMWare somewhat stable by re-installing GPU drivers (originally attempted to install the recent beta ones, which ended up breaking my APU thus leaving me with a power hungry GPU) and re-initiating some of the VMWare specific modules.
It's still awfully slow and crashes whenever I try to move a maximized program (i. e. Construct 2, which launches maximized by default) into Unity mode.
After that disastrous bit, I decided to give Virtualbox another chance and, lo and behold, I found the optimal settings (which is, basically, disabling all kinds of acceleration during the initial installation) to successfully install it.
It's pretty sleek and fast (especially in comparison to VMWare) and, after installing Guest Additions and runtimes (.Net, DirectX9, etc), I'm able to run many applications rather decently.
Seamless mode is rather broken on Compiz, unfortunately. With the Windows 7 Basic theme, I never get more than 1/3 of a window and with Windows 7 Aero, everything changes to a single color (including the text.
Strangely, OpenGL/WebGL content doesn't work 'cept in software mode or converted to DirectX. Google Chrome won't display any WebGL content and while Firefox is able to display most, it crashes whenever I try to access the WebGL samples hosted on scirra.com.
Tomorrow, I'm replacing the standard Direct3D implementation with a fanmade DirectX8/9/10 wrapper I found someplace else. After that, I'll pack everything I need into RemoteApps (requires Windows 7 Ultimate/Enterprise) and access them over FreeRDP (probably utilizing the Winconn GUI).
Overall, this seems to be the way to go. It's stable, performs rather decently and, with Winconn, I'll be able to add .desktop icons to my dock.