Can I play AVI files on Linpus?
Simple answer = No.
But it is possible
to install software which will do that for you. To do that you need to understand about codecs
. You also need to understand that there is a lot of politics that has been hidden from you - probably behind your dislike of Microsoft.
I'm on an ACER Aspire One with Linux Linpus
Acer deliver a light (read: incomplete) version of linpus with their netbooks - in some countries it is commandline only so you are lucky anything works at all. They have a history of shipping broken gnu/linuxes and there are a bunch of us trying to talk them around to behaving themselves.
You are pretty much expected (by Acer) to install another linux on this thing - or XP, or 7 - suggest UNR (Ubuntu Netbook Remix). You've tried Ubuntu before with little understanding dawning I take it? Gnu/linux does use a different paradigm from the regular proprietary model that bleeds into everything.
We do not normally recommend linpus for beginners precisely because it is difficult to understand. Adding to this, netbooks usually need a special implimentation which takes into account the limited resources. So you get a gui with tabs etc instead of the desktop you are probably used to.
all I want is to be able to watch videos, surf the net (no problems there) and convert the occasional file (maybe AVI to MP3 or 4 if that's an easier option than finding an AVI compatible media player)
Here you have the nub of the issue.
There is a video format that will play effortlessly in all gnu/linux distros. It is called "theora" and it has the suffix .ogv for reasons we need not go in to.
There is also an audio codec called "vorbis" which has suffix .oga
These formats are also html5 standards, and will play in html5-compatible browsers like firefox without needing a special player like flash does. In fact, you can right-click on any ogv file and have it play in your browser just like that.
Most distros have a program called "convert" which changes any format to ogv or oga via a mouse click. There is also a program called ffmpeg2theora which converts any Motion Picture Entertainments Group format (normally used in avi files) to theora or vorbis. Both these programs usually need to be installed.
The problem with avi and others is that there is often a royalty imposed on people who want to make players for them. Most gratis distros do not risk installing players because of this and other legal problems.
However, you could try linux mint or SimplyMepis - which do tend to ship with restricted formats. Of course, if you want to spend some money, you can purchase a commercial distro with this function built in.
However - no matter what, you are going to have to unlearn a lot of MS speak and learn a lot of linux speak. The price of freedom is hard work - you are always welcome to use a mac.