You will not gain anything by going back to the 2007 os ...
in fact...
I wouldn't use it unless the intention is for study of the 2007 os.
Using it will not net you greater or lesser functionality.
neither with issues pertaining to the 2007 os.
There was a reason why 2008 diablo 43-7 was done...
and there was a reason why cssu, asui, and diablo turbo was done.
It was to deal with lackings and issues on 2007 os

I would suggest you enable the proper catalogues in the app. man.
I would suggest you add gronmayers meta catalogue after deleting the existing catalogues and disabling the ones that are nokian.
I would suggest making sure you enable the 2008 catalogues of gronmayer. use the "install all" button
I would suggest going into the app man drop down tools catalogue settings and after waiting very patiently for alllllll the catalogues to update properly...disabling the n900 backport catalogues...and disabling the nonfunctional catalogues or delete them.
The app man will then be a bit faster updating...since it will not be trying to update broken catalogues...
And actually you should always be patient with the app. man. when letting it update...let it do it's thing...don't rush it.
Remember the ability of the n8x0 is still on par with a pentium 2 (if memory serves...) so for some things a little patience is needed..
especially when there is a huge list of catalogues that the system is trying to update and the scads of downloadable stuff in each catalogue also updating (let alone the system trying to resolve the list of broken catalogues ...if you have not disabled them...)
So it isn't that the n8x0 is tardy or slow or whatever.
It's sorting and dealing with a ton of information.
So when mucking about in the app man after installing and enabling gronmayer's ...be patient. Let it do it's thing... before taxing it more.
Or ...and people please listen here...
Or you will end up with needing to shut down and restart...
and then have to go back into the app man...

Let it process what last command you asked it to process...before asking more of it.
Otherwise the app man will rebel...
and it won't show the catalogues or their contents... properly if you are lucky.
and you'll be doing alot of time-wasting restarting...
going back to what you were trying to do.

If done properly you should have no problem installing fbreader properly and running it properly from the app. man.

Dealing with gronmayers meta catalogues is covered as part of the n8x0 walkthrough ....from my signature..
proper instructions are there...