I had intended to try this for some time but have only now gotten around to it. In the end, it really wasn't that difficult to get Mepis 8.0 installed on a 4 GB Kingston pendrive and booting with ease from the Ubuntu Grub on the mbr.
What I did was:
1. Download Mepis 8.0 from here
2. Reformat 4 GB pendrive to ext3 and create 2 partitions; 3.0 GB and 0.7 GB (both ext3)
3. Use Unetbootin and another pendrive (1 GB) to create a bootable LiveUSB from the downloaded Mepis iso
4. Boot to the LiveUSB pendrive and install Mepis to the pendrive (/dev/sdc1 --3.0GB-- /, /dev/sdc2 --0.7GB-- /home)
5. Create a new stanza in Ubuntu's /boot/grub/menu.lst as follows:
title MEPIS at sdc1, newest kernel
kernel /boot/mepis/vmlinuz-2.6.27-1-mepis-smp root=/dev/sdc1
Note that the menu.lst created within the Mepis / partition on the pendrive contains a simpler name for the vmlinuz and initrd.img files, but I couldn't get these to boot.
I also had to delete all of the additional options from the kernel line to get a clean boot.
Another problem I had initially was that while I could login as root without problems, when I tried to login as user, I got an error message saying
Could not start kstartupconfig. Check your installation
To overcome this, I had to go to TTy1 with Ctrl-Alt-F1 and then create the /home/paul folder which was missing.
Next I issued the command
chown -R paul:users /home/paul
After this, I could boot as user without problems.
After several successful boots, when I tried to boot into Mepis this morning, it wouldn't boot seemingly because it couldn't find the appropriate file system.
So, I booted to Ubuntu and ran
fsck -y /dev/sdc1
and this said that the FS on this partition had lost its journaling system and was now effectively a ext2 system. However, it proceeded to fix this problem and restore the ext3 FS without any harm to the installed OS. After this, it booted as before.
While the eth0 connection was available out-of-the-box, I didn't have a wireless connection.
This required installing the available rt2860-modules package from Synaptic and, subsequently moving the resulting rt2860sta.ko module from /lib/modules/2.6.27-1-mepis-smp/misc to /lib/modules/2.6.27-1-mepis-smp/kernel/drivers/net/wireless.
After a reboot, I then ran
Now #iwconfig showed ra0 as an available interface.
Next I ran iwlist ra0 scan to scan for aps. This identified "dlink" as an available essid.
Then I ran iwconfig ra0 essid "dlink" and finally
in order to get an IP address for the connection.
Now wireless works perfectly although I need to run the dhclient command after every boot. However, this should be very easy to fix.