Yes, you need a high spec computer to get games to run good on a virtual install. Assuming that XP is your virtual install, you'd need to be able to lend the 3.25GB of RAM that the OS can address. Without allowing your host OS to drop below the specs it needs to run, 2GB RAM for 32 bit, 3GB for 64 bit. These specs are higher than what MS publishes, but in real life, 2GB is not quite enough for a 64 bit Windows 7 install to run good.
Plus, there's the CPU to consider. You'll need at least a dual core CPU that runs at 2.5GHz to get any kind of decent performance in doing what you want, probably more.
Virtual machines are good for many things, they can save a company or a home user money, by minimizing hardware investment. Meaning that one can run several OS's on a single computer, 2 or more at a time. I know of a few people who uses virtualization for different things, but not gaming. Very seldom does this issue arise.
If you can't get the games to run, then you need to go into the settings & lend as much RAM as you can afford, and allow for 2 CPU cores. This will prompt you into another setting that you'll have to change, enabling ACHI, as I recall. You'll be shown the improper configuration when you enable 2 CPU cores. And keep in mind, once you set this as such in VBox, there's no turning back, except a reinstall. Unless you have a recent backup of the partition that the VM is on.
Most of what I wanted to do was just see if I could do it. It appears as though I may be able to, but with significant effort. And my computer doesn't seem to have the hardware requirements. I'll scrap the whole game idea, the real reason I have a virtual windows machine is to use a couple programs that can't be run on mac or linux.