Hmm. Thats a very small budget you got there.
I think your best bet is to buy a DIY Combo + a graphics card. You can save some money by building the computer yourself.
This is a very weak computer, and I don't think you can do too much with it. With that budget and the video card I recommended, you should be able to run TF2 fine. But no guarantees on highest graphics.
I know you said no used, these aren't used PCs I can get you. They are off lease business PCs that are fully refurbished with a fresh install of a new copy of windows 7 & warrantied. You would have 2 add a graphics card but I can get you 1 with a similar processor starting in the low $200's including shipping 2 your door depending on how much ram & the size hard drive you would want. If you want more info either email me @ Wicked_Systemz@WickedSystemz.com or visit our website Home - Wicked Systemz I have 12 off lease systemz for less than $300 listed all dual core processors with Windows 7.