Umm do some more research since I'm not an expert, but the basics are below, and I'm not responsible if your phone bricks. LOL, don't know why everyone puts that disclaimer, has someone sued another former member or something? Anyways ya, do at your own risk.
check out this:
http://androidforums.com/vibrant-tips-tricks/223806-guide-fixing-bricks-odin-errors.html
and check out this:
http://www.youtube.com/watch?v=uGMDycXJ2i0
If you want to a 5 yr old to teach you ODIN and you understand what the heck he is saying, then watch this. (just found it, and can't stop laughing...I don't know why but I think it's funny) Most of us grown folks don't know how to use odin and this little kid does.
http://www.youtube.com/watch?v=SOC7psum2_Y
The first link I provided, you can download everything from there, but here is a newer version of odin I'm uploading on sendspace for you. I put up the pit file also so you don't have to extract it. All you have to do is download the tar (too large for me to upload) from the first link.
It is safe to go from 2.2 directly to stock JFD using ODIN, if you have never messed with partitions or applied any lagfix. Otherwise, if you have screwed with partitions or applied lagfix, I believe you need to first install "eugenes froyo that doesn't brick" which will fix your partitions, then you can ODIN back to stock JFD (the version that shipped in the box).
Steps.
1) Download odin, JFD tar, and JFD pit.
2) Open odin first. (phone not connected to computer yet).
3) Turn phone off
4) Hold down vol up and vol down at same time (dont touch power)
5) while holding down volume buttons, plug in USB cord into phone (connected to your computer on the other end)
6) your phone will go into download mode (yellow triangle with android man holding a shovel)
7) assuming you have proper drivers pre-installed or (samsung kies installed which provides the drivers); in this case Odin will recognize your phone
8) in odin, a yellow box will appear with a "com" followed by any number.
9)in the pit section, inside odin, click on pit, and find the pit file wherever you saved it on your computer.
10)PDA section, click it, and put the tar file there.
11) leave csc alone.
12)auto reboot and f.set.time will have check marks
13)re-partition leave unchecked.
14) press start
Give it a few mins, and it will be done and your phone will reboot, and you can remove the usb cord only after it successively finishes. You're phone will now be in brand spanking new stock JFD condition. Next, you can put any new rom on it you like, or if you want JI6 back, just use kies mini, to update the firmware to JI6.
Below are the sendspace pit and odin files I uploaded, but get the JFD tar from the first link.
pit: (already extracted for you)
Download s1_odin_20100512.pit from Sendspace.com - send big files the easy way
odin3 v1.70:
Download Odin3 v1.7.exe from Sendspace.com - send big files the easy way
tar:
use the 1st link above to download the JFD tar.
Remember it is safe to go from 2.2 to stock 2.1 using Odin and the process above, as long as you have never screwed with partitions or applied lagfix or voodoo or whatever, in that case, you need to use "eugenes froyo that doesn't brick" first, then ODIN.