Few tips:
MBR - (master boot record) - First sector of HDD. Bios is loading it firstly, and starts program on it. It contains information about primary partitions and start address of extended partition.
Boot Record - first sector of any partition.
Lilo - program to load Linux (LILO== LInux LOader), also can start other OSes and DOS.
Lilo has two parts - first is program under Linux - It has config file lilo.conf, as a rule it is located on /etc/ dir. You write configuration to this config file, then start lilo and it is writing boot loader accordingly with lilo.conf . Second lilo part is this boot loader.
You can config dual boot system by these two ways :
1. Write Lilo to MBR - so, you will need to point lilo.conf to your Windows partiton and to Linux main partition.
2. Write your additional loader - as you say, you want to use "boot magic"; I was using "System Commander" for this purpose. In this way, you need to write Lilo boot loader on Boot Record of your Linux partiton.
Again, for second variant, it will be so: MBR will have your System Commander. Linux partition will have Lilo on its Boot Record. Point your System Commander to Linux partiton, and it will find Lilo on Boot Record of that partiton.
You will need install in this consecution:
1. Install your Windows.
2. Install your System Commander loader on MBR, configure it to load Windows.
3. Install Linux, when linux install program will ask you about boot loader configuration, point it to Boot Record of linux partiton. Write only one instance on lilo.conf - do not configure Lilo for Windows or DOS loading.
4. After all, when your machine will reboot, point your System Commander to partiton with linux.
Ok, I was writing about System Commander, you can try to use your Boot Magic for this - probably, it will work the same way.
Anyway, it is good rule to have windows rescue floppy disk. Also, better to have Linux rescue diskette. You will need to make it before linux install. Search on the web recue diskette image and use RAWRITE.EXE DOS utilite to write this image to diskette.