No guarantee that the HP keyboard would work with the iPad but I see no reason it would not especially since a variety of other third party bluetooth keyboards work well with the iPad.
As far as other alternatives are concerned, take a look at the Microsoft 6000 Bluetooth Mobile keyboard. It's less expensive than the Apple Wireless, is better designed from an ergonomic perspective, and includes a separate 10 key number pad (also bluetooth) if that matters to you. (You can get the keyboard alone for even less than keyboard+number pad from several resellers, including buy.com.)
It's slightly wider than the Apple Wireless keyboard but fits easily into a backpack or bag. I've used mine with both my iPad and my laptop. Though it's a plastic frame, I've found it travels very well. Pretty much indestructible.
If I didn't use the Incase Origami Workstation as both a case for the Apple Wireless keyboard and a stand for the iPad I would have stuck with the Microsoft keyboard. It's a very good product.
P.S. Happened to notice that a customer has added a photo of the keyboard with a tablet on the
Amazon site. Gives a very good perspective on its size relative to the iPad. See the second link below.
[ame="http://www.
amazon.com/Microsoft-Bluetooth-Mobile-Keyboard-6000/dp/B002NP8XJ0/ref=sr_1_2?ie=UTF8&qid=1309870918&sr=8-2"]
Amazon.com: Microsoft Bluetooth Mobile Keyboard 6000: Electronics[/ame]
[ame]http://www.
amazon.com/Microsoft-2XJ-00001-Bluetooth-Keyboard-6000/dp/B004HVW0ZQ/ref=pd_cp_e_1[/ame]
