Please, test new version of xarchiver. Download right now from cooker: http://cook.slitaz.org/cooker.cgi?download=xarchiver-0.5.3.tazpkg (it will reach regular repository only on next sync, maybe tomorrow or so).
Added new configuration page to xarchiver. You can display it using xarchiver's menu → Help → Contents, or just pressing F1 on your keyboard.
Really xarchiver is a wrapper. And it can support many archive formats. But it can support, let's say, rar archive format, only if you install rar package. And here you can install (and remove) a supplementary packages for archive formats you want.
When you press “Install” (or “Remove”) button first time you'll be prompted for Username and Password. Don't be afraid :-) Here invisible TazPanel installs and removes packages for you.
Please check general work.
And please proofread text, because my English is far from good. Maybe you can write more clear?
Or you can provide more elegant solution?
Please don't hesitate! Write me pair of lines here.