Ivy Bridge i3 parts are due out in September, and the one to look at is the i3 3225. It is supposed to feature HD 4000 graphics which will be plenty enough for any streaming your father will be doing, and even some fairly light gaming. Granted, HD 3000 is probably enough (I'm running that on my CustoMac and can use two monitors + stream video on one of them just fine, can play Minecraft and TF2 at acceptable frame rates (though not perfect)), but HD 4000 is the best you can get integrated from Intel at this point.
While KefkaticFanatic has issue with AMD, there really isn't anything inherently wrong with them. And for a budget build, their integrated graphics are still better than Intel's in most cases, even though they're at their last-gen parts. They acquired ATI a few years back, so they have real GPU power on their products, so if you were to be gaming, the driver support would be there. Their APU (Accelerated Processing Unit, which has both CPU and GPU) solution isn't a great option if you're adding a dedicated video card as the CPU performance isn't as good as Intel. However, if your dad isn't gaming, it's a very viable solution.
Here are two possible builds, one from AMD and one from Intel, both of which should suit your needs just fine. If you wanted to add a graphics card for actual gaming at some point, I'd definitely choose the Intel system. If you're content with low/mid gaming now and aren't overly interested in adding a graphics card later, I'd pick the AMD system. You can definitely add one in either case, but the Intel system will have more CPU power to offer if you no longer require the integrated GPU.
PCPartPicker part list /
Price breakdown by merchant /
BenchmarksCPU: AMD A8-3870K 3.0GHz Quad-Core Processor ($109.99 @ Newegg)
Motherboard: Gigabyte GA-A55M-DS2 Micro ATX FM1 Motherboard ($49.99 @ Newegg)
Memory: Patriot Viper Xtreme 8GB (2 x 4GB) DDR3-1866 Memory ($56.99 @ Newegg)
Storage: Western Digital Caviar Blue 320GB 3.5" 7200RPM Internal Hard Drive ($68.98 @ Newegg)
Case: Rosewill RANGER-M MicroATX Mini Tower Case ($24.99 @ Newegg)
Power Supply: Antec 400W ATX12V / EPS12V Power Supply ($19.99 @ Newegg)
Optical Drive: Lite-On iHAS124-04 DVD/CD Writer ($21.98 @ Newegg)
Total: $352.91
(Prices include shipping and discounts when available.)(Generated by PCPartPicker 2012-08-21 09:27 EDT-0400)PCPartPicker part list /
Price breakdown by merchant /
BenchmarksCPU: Intel Core i3-2105 3.1GHz Dual-Core Processor ($134.99 @ Newegg)
Motherboard: Gigabyte GA-H61M-DS2 Micro ATX LGA1155 Motherboard ($49.99 @ Newegg)
Memory: Mushkin Silverline 8GB (2 x 4GB) DDR3-1333 Memory ($44.99 @ Newegg)
Storage: Western Digital Caviar Blue 320GB 3.5" 7200RPM Internal Hard Drive ($68.98 @ Newegg)
Case: Rosewill RANGER-M MicroATX Mini Tower Case ($24.99 @ Newegg)
Power Supply: Antec 400W ATX12V / EPS12V Power Supply ($19.99 @ Newegg)
Optical Drive: Lite-On iHAS124-04 DVD/CD Writer ($21.98 @ Newegg)
Total: $365.91
(Prices include shipping and discounts when available.)(Generated by PCPartPicker 2012-08-21 09:33 EDT-0400)Just a note, both of these are fully NewEgg compatible builds. If you purchase from separate / alternative places, you may save money. Regarding the Intel build, I would wait a few weeks for the Ivy Bridge processor I mentioned earlier. You'll get better GPU and slightly better CPU performance.
Regarding the AMD build, I included better memory because the APU greatly benefits from the higher bandwidth (specifically, the GPU portion). Also, if you're willing to wait until October, the next-gen products are due out. They are supposed to be a pretty decent bit better on both CPU and GPU, with the CPU getting quite the boost. The next-gen products won't be compatible with the current boards.
Also, I believe both have various rebates, so it's just something to consider.
Both of these builds have one HDD, and you could add a second if you so desired for backup or alternative uses. If he has a monitor from 4-5+ years ago, I'd also be tempted to find a ~$120-150 1920x1080 LED backlit monitor since that would be noticed as an upgrade as he would be looking at it whenever he uses the computer. Similarly, if he has a junky old keyboard / mouse, I'd consider a new one of each since they get the same usage as the monitor. Nothing high-end, just something new / clean.