how can i format a usb to work with windows vista on mac

Windows cannot read Mac formatted drives. If you used Disk Utility on the Mac side, then the drive is not usable by Windows. You need to format the drive either NTFS or FAT32 if you want Windows to see it.

OSx cannot on its own write to NTFS drives, but can read from them. Both OSx and Windows can read and write to FAT32 formatted drives.

You should be able to format the USB drive to NTFS or FAT32 from Windows.

Windows will read and write to a drive formatted for Mac at the USB port of the AirPort Extreme as a FAT32 volume. Don't know what will happen though if there are already files on the USB drive before it is connected the AirPort. Haven't tried that.

All things considered, things would be a lot easier if the OP added a USB to the AirPort that would be used only for Time Machine backups.....as he was asking in his other similar post.

I suggest that you give Paragon NTFS for Mac a look at. They have a free 10-day trial.

This is VERY SIMPLE to do with the mac alone - no need to format the drive in Windows, and most certainly no need to install other software like Paragon.

The simplest solution would have been NOT to format the thumb drive at all. They are usable on both mac and windows out of the box.

As you have formatted in a way that is "mac only", all you have to do now is to reformat it, In Disk Utility, in the right way.

You can choose either FAT32 or ExFAT.

Here it goes, step by step:

1) Select the whole drive (not the Volume inside - see the picture), click on Erase and fill it as shown. You can of course name it any way you like (sort of).

You can choose ExFAT instead of FAT. The main difference being that ExFAT can have files larger than 4GB, while FAT cannot.

2) Wait, there is no step 2...

Something to keep in mind, Windows Vista does not natively support USB 3.0. Nor did Windows 7. There are 3.0 drivers for Windows 7. Not sure about Vista.

Is Master Boot Record the scheme I should choose to make it work on both mac and windows?

Yes.