Your best bet is to get Droid Comic Viewer from the Market, first. VASTLY less likely to crash on your phone than jjComic. Actually, jjComic is terrible in comparison to Droid Comic Viewer (which shows as ACV in the app menu on your phone).
Once you have that installed, your next move would be to convert your CBR files to ZIP or CBZ. ACV will open CBR/RAR files, but CBZ and ZIP work far better and operate much faster.
So, what you'll first do is navigate to the folder on your computer containing your CBR files. Don't actually OPEN the folder, though. Press Shift, then RIGHT CLICK on the folder, and click on "Open command window here". This will open that folder in Command Prompt. From there, enter the following command:
This will mass-rename ALL your CBR files to RAR, thus enabling WinRAR to open them. Once you've done that, you'll use WinRAR to convert them all to ZIP files. To do this, first you'll have to do the right settings in WinRAR. Go to "Options", "Settings", then click on the "Compression" tab. There, click "Create Default". On that window, switch RAR to ZIP, then change compression method to "Fastest" (unless you want to waste time converting). Click ok, then switch to the "Integration" tab and ensure that "Integrate WinRAR into shell" is checked. Click ok, then click ok again to finish working on settings and go back to WinRAR itself.
Now click "Tools", then "Convert archives". On the right side, ensure that rar is checked. Now click "add", and add all the files you want to convert. Press shift and click on the first, then click on the last and it'll select ALL of them, so you don't have to add them one-by-one.
Once you have them all selected, you can convert to ZIP. If you don't care to keep your originals, you can set it to delete them all (I'd do this, conserves space). Click Ok, and it'll convert them all.
Once you have them converted, you can now rename them to CBZ from ZIP if you'd like (but this is unnecessary - ACV will use them in ZIP format), using the Command Prompt method I explained above, just change the command to the following:
Now all your files are in a format that pretty much all comic book readers can use at a much faster pace. Upload them onto your memory card, open 'em with ACV, and enjoy!