It is hard to tell for sure how TF2 will perform on i3 HD2500, but You can check external cards from these charts and look for how they perform in TF3. I presume You could get something like 30fps at low to middle.
Performance of 2500HD should be the same on i3 and i5 as Intel gives same spec for graphics:
Processor Graphics Intel® HD Graphics 2500
Graphics Base Frequency 650 MHz
Graphics Max Dynamic Frequency 1.05 GHz
Integrated graphics usually won't get you far - this is no exception. In this case you'll probably be able to play, but only on very low settings. You'd be better off buying a really cheap graphics card (maybe a second hand 8800GTX or GTX240, looks like they're on eBay for about $30) since you'll be able to play at higher settings, and play some other games too.