I just upgraded the ROM on my 300Mhz X5 from A00 straight to A05,
LEGITIMATELY. :approve: This AximUsers thread (LINK REMOVE) proved very helpful. The crucial info and helpful links are on the first page of the thread. One thing I learned is that when you hold the four button combo to trip the ROM replacement process, hold all four (POWER + RESET + SCROLL + CONTACTS) and release POWER and RESET after only 2 seconds (so as to prevent it going into a hard reset), while continuing to hold the other two. Good luck!
EDIT (GRENTZ): That is not a legal way to install it, sorry but all you are doing is using a rom you got for free and tricking your X5 into installing it. You never purchased the license that is required to make it legal.