alright, to get to exhentai, u first need to have an account on the main site,
hxxp://e-hentai.org/
then, once ur logged in, it should let u in without the sad panda.
if the panda still shows up, then u can try 2 things.
first, there are 2 plugins made for both firefox and chrome that once installed you it will ask you for ur log in information at the exhentai page to get in.
firefox plug-in:
hxxp://haruhichan.com/wpblog/index.php/1039/exhentai-firefox-plugin-get-past-sad-panda.html
chrome plug-in:
hxxp://haruhichan.com/wpblog/index.php/815/exhentai-chrome-plugin-get-past-sad-panda.html
then there is the way where you can edit your cookies to get in. to do that, u need a cookie editor extension for your browser.
Then: look for, under the cookies under the 'e-hentai.org' domain, that are labeled, 'ipd_pass_hash', and 'ipb_member_id'. <-- u need to add these to the 'exhentai.org' cookies.
u have to at least tried to load exhentai's page so it will show up in ur cookies/the cookie editor. So! you should see an exhentai cookie labaled 'yay' (cocky bastards, right? lol) so select it, change it's name to 'ipd_member_id' and copy/paste it's content (should be 6 numbers) into the content bar, then save it.
next, add/make a new cookie under the exhentai domain, name it, 'ipb_pass_hash' and copy/paste that cookies content (also from the original on the ehentai domain) into the content field and then save.
you should now have duplicated both the 'ipd_pass_hash' and 'ipb_member_id' cookies from the 'e-hentai.org' domain, into the 'exhentai.org' domain.
^to make it even more effective, you can change the expiration date to something like the year 2100 like i did XD
also im really sorry if that was confusing, please let me know if anyone needs clarification