You would need to update your graphics card if you wanted to use the aero interface. That being said you can simply not use the aero interface. That would be your easiest solution. You would still have windows 7 except it would look more like windows XP if you had aero turned off. You also may find that windows 7 does not run well on your machine due to it's age.
I believe your computer came out almost 10 years ago which in computer terms is ancient. So I would not be surprised if you had other issues aside from the aero not working.
My advice would be to not put anymore money into upgrading a 10 year old computer but rather save up for something newer. If you really want to upgrade your video card you would need to find yourself a PCI Express x16 video card which is what would fit your motherboard.
But as I said, I really would not recommend buying new hardware for a computer this old because if with a couple hardware upgrades this machine will likely run better with windows xp than it will with windows 7 no matter what you do. Windows 7 needs better hardware than an older xp machine so if the upgrade adviser tells you it will work it does not mean it will work well.
My professional opinion is that you hold off upgrading this system anymore and save up for something new. You can get a brand new computer that would be far better than your current one for as low as $350.
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