It seems that U 10.04 has better ruby support than 10.10.
Should I downgrade? Would it be a lot of trouble?
If I do want to, what is the best way to do it?
I basically know nothing about server admin...
Both Ubuntu 10.04 and Ubuntu 10.10 have a full suite of Ruby utilities available from their package management system. I highly doubt they've supported less Ruby features as time has gone on so it's likely you just need to install the tools/libraries you need.
If you're using the GUI, you can look into Synaptic Package Manager to find various Ruby packages. If you have only access to the command-line, commands like
apt-cache search and
apt-get install are your friends. There is also the interactive command-line program
In addition, if you have some reason for having 10.10 in the first place, you can install custom versions of Ruby either by downloading and installing them from source (this will take some learning if you're starting with no basic knowledge of systems administration, but is achievable), or using a tool called Ruby Version Manager.
If you have no reason for using 10.10 currently, @Zoredache is absolutely correct and you should check out 12.04.
The only supported way to downgrade is to backup, format, and re-install. The amount of trouble this would be completely depends on how well you have documented your setup procedures.
Ubuntu 10.10 does not have long-term support and will not recieve security coverage after April 2012, so you should strongly consider either upgrading to a more recent release or going back to 10.04. A new LTS release should be coming out very soon. It might be stable enough now, that you could upgrade and start using it now.
If I were actually going to do this, I would use apt pinning to force old packages to replace current ones and current ones to be uninstalled if they have no replacement. I'd then cry a little inside when obsoleted packages are not replaced with their older versions because they've been removed in the newer release. I'd probably spend some time fighting with impossible dependency loops and having to fix them with manual wielding of dpkg.
You may want to force-downgrade some select packages related to ruby, but beware that his can make a hell of a mess. Unless you really know what you're doing, don't.
Whether the older packages will work with newer base libraries isn't a guarantee. If that's the case, consider learning how to compile packages from source if you want to work on a specific revision. That will allow you to get the version you want without possibly having to downgrade major system libraries (and, in turn, everything that uses them).
... but really, tell us what the actual, direct problem is. I think most of us suspect your root cause analysis and action plan are poorly chosen.