Boo,
Husse, thanks for your answers!
Boo wrote:first you need to set your bios to automaticly choose the ide drive to boot off, and not choose it manually each time (not really important just saves time and can help find some bugs/features).
Generally, I have Vista installed on my 320Gb SATA HDD and don't want Linux make any changes in it's MBR (just as much as don't want Vista to make any changes to Linux's 40Gb ATA HDD). My idea was to make its own HDD(with it's MBR) for each OS and select what to boot via Boot menu. I didn't want any of OSes to know anything about eachother. It's easier to maintain them. I could have had: Vista boots by default from 320Gb SATA HDD and Mint boots only after I manually press F8(on my motherboard) and select it's 40Gb ATA HDD to boot from. But something is wrong here

Boo wrote:by the sounds of it your sata drives (ie sata controller) are discovered before your ide drives
You know, when I connected my SATAs after installation and faced the problem - I've assumed that the problem can be the order of disks or something. But one thing surprised me: how it can START loading the system(showing blue logo) and load BusyBox if he can't locate proper disk to boot from? I mean - it loads something, it loads BusyBox, but then can't find some other files... Where did it get the ones it already loaded from??
And one more thing: I assume that if I install Linux Mint with NOT changing any of hardware before, during and after install, it should ALWAYS load fine. It was very strange for me that it didn't load even after I reinstalled it with all HDDs connected. I think it should have analyzed all the hardware I have and order of HDDs I have. Just IMHO.
About your solution - thank you again, I'm just going to reboot now and apply it. Will edit my post with the result.
ADDED: Thanks,
Boo, your solution helped. I just changed sda to sdc and it booted with no problems. Then I changed menu.lst in Root/Boot folder (there are no boot folder in etc somewhy... But I remember that it was there when I used Mint 5 with Gnome). Thank you very much!
P.S.: Thank you again for maintaining and keeping developing Linux Mint KDE. It's really great, honestly.