|It appears there is some confusion between concatenated volumes, which is what the poster is kinda of asking about, and that of raid 0 volume.|
A concatenated volume is one that links different drives together as one volume. This is referred to as a spanned disk. Some newer definations also list this as jbod [just a bunch of drives]
You can think of a concatenated volume as a bunch of barrels all connected at the top with a pipe. The first drive filles up and then data spills over to the second drive and so forth for each additional drive.
This is not the same as a raid0 stripe which has data split into blocks on each drive.
A spanned volume has the same risk at a raid0 volume.
I believe Partition Magic has the ability to do spanned volumes but since I have only used them in training/practice I can not say for sure that PM can do it.
Do note that you have to remove all data from both disks to then create the spanned volume, then restore. It's just like initializing a raid array wipes all data off the array.
I suspect this was not the answer you were looking for concerning your question. There is no easy way to make two data volumes appear as one on a local machine.
You may want to investigate ntfs junction points.