Thanks for all those who posted replies to help.

I have a spare USB key which has already my stuff on it (music, programs, etc) and I decided to use that in order to boot BootTrack v3. OK, so I installed BTv3 on it, without recreating any partitions or all that, and it worked. No surprise, it just updated the MBR to reflect booting into BT3 on a reboot (thats as long as you leave the "boot" and "bt3" under the root directory of your USB key). Ok, now comes the part where am not sure about:

If I want to use that same configuration but let BT to write changes into /dev/sda1 (I dont want to have a second partition), will that work or I will need to create a folder called changes and point BT to /dev/sda1/changes? Basically, since I can write things to /dev/sda1, which is also the root directory of the USB key, why would should I not be able to write changes on that same partition? I think its possible. Any one have tried this? I will do some tests and report results, but if anyone already tried it, please let me know. Thanks.