iDVD, DVD -R and DVD +R

I have iMovie 5.0.2, iDVD 4.0.1 and the following Superdrive:

PIONEER DVD-RW DVR-107D:

Firmware Revision: A707
Interconnect: ATAPI
Burn Support: Yes (Apple Shipped/Supported)
Cache: 2000 KB
Reads DVD: Yes
CD-Write: -R, -RW
DVD-Write: -R, -RW, +R, +RW
Burn Underrun Protection CD: Yes
Burn Underrun Protection DVD: Yes
Write Strategies: CD-TAO, CD-SAO, CD-Raw, DVD-DAO
Media: No

I made a movie in iMovie and transferred it to iDVD. I inserted a blank DVD +R disk, but the drive spat it out and iDVD said 'Insert a DVD -R disk'.

As can be seen from the above extract from my 'About this Mac', my drive will burn DVD +R disks; and, indeed, I subsequently successfully burnt my movie onto a DVD +R disk by using Toast Titanium.

I should like to ask four questions:

1) Am I right in deducing that it is my iDVD 4.0.1 that is balking at the DVD +R disk and not my burner?

2) As I have bought a pile of blank DVD +R disks, it would be good to be able to use them, and I like using iDVD. So is there a later version of iDVD that will burn DVD +R disks?

3) If the answer to 2) is 'Yes', from where can I obtain such a later version without buying the whole of iLife '08? (I say '08, because my OS X is Tiger, not Leopard.)

4) What are the relative advantages and disadvantages of +R and -R disks?

Thank all you experts very much in anticipation of becoming educated.