Why exactly is sda5 unwanted? Is it because of the high number?
When installing Trisquel, I usually setup one (small) primary partition (/) and one (very big) logical partition (/home). Swap is usually a couple hundred MB big (depends on different factors) and sits at the end. The /home always comes out as sda5. I believe this is perfectly normal and not an error on the part of the installer. In order to create a new logical partition an extended partition has to be created first, which takes up one number (so you have sda1 for "/" and sda2 for the extended partition, which isn't usable by itself). Then two numbers seem to be reserved for something, so that the first logical partition that can be automatically created is sda5.
You may find it interesting to learn more about partitioning of hard drives here.
Here you can find information on partitions specific to Ubuntu (which is the base for Trisquel). Be aware, that Canonical has different views on software than this community and will call the OS Linux (instead of GNU/Linux) and they also don't oppose non-free software as much. But the technical aspects are all the same between Trisquel and Ubuntu.
