Since you are using an Arduino a .NET app isn't going to be much help unless you can get the source code and use that as a reference. .NET can be used on Arduinos but you are probably going to get stuck, because there will be less examples. (The source code will probably be in either C# or VB and if you can read Arduino C you can read them)
"Do the sensors create an image?" Yes and no. From what I can see from the data sheets you have a number of pixels that have analog values. These values are stored in memory on the sensor and you use I2C to read from that memory.
There are I2C libraries for an Arduino. There is probably an I2C library to interface with the memory chip. There might even be a library to talk to the sensor. However the most difficult part will be converting the pixel values into something that allows your Robot to 'see' a heat source, this will take some research on how to do it.
The sensors have different numbers of pixels. Having 64 pixels is fine, but how long will it take an Arduino to read 64x16bit numbers over an I2C interface and then evaluate the data and make a decision on which direction to move. I think you should be looking at a multi-microprocessor system.
Which sensor is better? Personally I would go with the Omron mounted horizontally. My reasoning isn't just the cost, the RoBoard wants 2.5-2.7V and that is going to be harder to regulate than the 4.5-5.5V that the Omron wants when you are running on batteries. The 1x8 sensor only has a 6 degree vertical angle, but it has much higher resolution that the 4x4. One possible option might be to have one of each and perform a gross search with the 4x4 and the focus in with the 8x1 sensor.
You are probably going to want to have the ability to rotate the sensor and pan it vertically to allow the robot to look around the room. Then stich the data together to get the bigger picture.
Hope that helps