I'll leave the Linux Solutions to the Guru's but i can explain the boot process for you.. or at least attempt to....

When you power on the first thing that happens is your computer runs it's POST (Power on Self Test.
ROM BIOS Startup program checks out hardware resources and needs and then assigns system resources (IRQs, DMA Channels, I/O Addresses and Memory Addresses). Then it begins the start-up process by gathing all your config information from various sources (DIP Switches, Jumpers, CMOS Chip) and compares it with your hardware that's installed.
The next step is for the ROM BIOS Startup program to find the OS (For this we'll assume an floppy, hdd boot order with no floppy inserted)... The Bios looks to floppy and finds nothing so then it turns to the hdd. The Bios talks to the MBR (Master boot record)
-- Side Note -- The Layout of your harddrive is Partition Table which contains The MBR Followed by Information on your logical drives followed by the identity of the boot drive. Then your drive starts (or firstr drive if it's partitioned) this begins with your OS boot record. Followed by the rest of the hdd
--End Note --

The MBR turns to the HDD and attempts to find the OS Boot record. in the case of DOS (simplicity at it's best) It finds the OS Boot Record, which in turns tries to find the boot files (For dos - IO.SYS and MSDOS.SYS.... )If it successfully finds the boot files then the OS loads and takes over, loading it's drivers and software and anything else it needs.


Anyways there's a basic breakdown of how your computer boots.