First off I'm hesitant to call the Iraqi Dinar an investment, I personally would call it high risk speculation. I look at it like a longshot lottery ticket than an investment.
As to your question though I own the Iraqi Dinar as well as the Vietnam Dong. I purchased my Dinar way back in 2004 and the Vietnam Dong more recently.
Some people think that the dinar they bought for say $1000 is going to revalue or rv as they call it and be worth anywhere from 3 million dollars to 12 million dollars overnight. I personally don't believe this is possible, the numbers don't back it up, there's never been another revalue in history anyone can point to, and lastly the old rule if it sounds too good to be true it probably is.
That said if Iraq can stabalize economically, financially, and politically and get that oil industry going it's possiblle the currerncy will go up in value and people can make money.
If your considering buying the dinar you have a few options. There's few if any banks or brick and mortar currency exchanges that deal in the Iraqi Dinar so for buying you can buy from online dealers, ebay or from other members of forums like Dinar Vets selling off their personal stash.