Not really. The 9800GTX+ is still WAY more powerful than HD 4000.
The only thing the iGPU is good for when you use a discreet card is Quick Sync for video encoding when you use VirtuMVP. VirtuMVP supposedly helps gaming performance a bit, but I haven't really seen anything to back that up.
And no, there are no "hacks" to make PhysX work on anything other than a Nvidia GPU.
Lucidlogix's Virtu software will allow you to use the SB/IB IGP and your discrete graphics card at the same time. I haven't personally used this, so I cannot vouch for its quality. But I have read highly regarded reviews of it. http://www.lucidlogix.com/product-virtu-gpu.html
I'm surprised your motherboard DVD didn't come with a copy of it.
Actually, it did. The only driver I install from a preset source, though is my wireless adapter. Followed by Waterfox. Then I just download all the latest ones.
I'll have to read that review of Virtu. Because from what I've seen from other users, it takes about a week of constant tweaking to get it to function, and then it's glitches galore once it actually runs.