It is really unfortunate that you have not been able to install linux on your computer yet. But nothing is lost. there are more ways to rome than one.
So let us take stock of the suituation. Firstly, if your computer won't boot from the cd, check whether your bios has been configured to try to boot from cdrom first. this subject has been discussed in this forum umpteen times.But still let us recollect. Ihope you no how to coonfigure your bios to boot from cd. If not here are some general rules.
1. almost all bioses have a key for invoking bios setup just as the computer is starting. On some computers the bios waits for a few seconds after POST and looks for the bios key press. The most common keys used for bios setup are Del, F1, F2, F10, and F12 (rare). so you will have to be fast and observant here. Keep a watch for the bios set up wait screen ( this varies vastly from computer to computer and is impossible to list all here). But whatever it is it will be there so just keep a watch.
2 And again the bios screen itself varies from system to system. But you will find the various options clearely ( In branded computers or assembled computers with branded motherboards (Intel, compaq, ASUS, Gigabyte etc) the screen will show a tool bar at the top. One of them will show "BOOT OPTIONS"). click on it and scroll down or use arrow keys to select cd rom as first boot device. save the settings via save and exit column and restart your computer.
3. Changing your boot disk order WILL NOT HARM YOUR WINDOWS XP. period.
Also Mepis does not come with Gparted. It comes with QT parted. Again if you are careful at the time of partitioning using QT parted ( an easy way is to first note down the disk size of all your windows partitions. In QT parted these will show up as fat or NTFS partitions with their size and usage indicated. You certainly cannot make a mistake here.) If you are still unsure just create an un allocated space using windows disk management tool ( you will find it in windows>system 32>dskmngmnt.) For this first move all the files from one partition to another partition and delet the now empty partition.care full here. check thoroughly that the partition does not contain any windows sytem files. use "show hidden files from folder options in control panel " create a new slightly smaller partition ( a partition of a mere 3 Gb is ample for Mepis. But the size again is your choice ).with the same drive letter and the same formatting (FAT or NTFS whichever it was earlier). Now you have an unallocated space on your disk. In QT parted select this ( it will show up as free space).click on it and click on Create in the drop down menu. again click commit in the Device menu. ( if you dont commit the partition will not be created). it will ask for confirmation . confirm. Mepis will auto allocate partitions for /(root), ?usr and swap (linux virtual memory). close QT parted and get back to installation. If you scroll down on the "install on button You shoud see the new partition as " hda ----whatever size you created with the format type (EXT 2 in Mepis 3 and EXT 3 in Mepis 6) click on it to bring it to the install wibndow. and click Next. It will again ask for confirmation to format the partition. Confirm and your Mepis installation will begin. Given the ststistics of your system it should take less than 20 minutes for installation to complete. At the end of installation, it will ask for the GRUB location Default is MBR. choose it. ( other choices are floppy and root folder of linux) set user password and root password and time zone etc. and reboot. your Mepis should be ready.
As for your information that partition will convert your D driuve (partition) to C, it is something amusing. There is no "C" drive, "D" drive etc in linux. In Linux drives are indicated as hda1, (the first partition on the first IDE), hda2, hda3, hdb1, hdb2 etc ( the second drive on IDE) for IDE disks and sga1, sda2, sdb1, sdb2 etc for serial drives ( USB drives and SATA drives). If you have not tinkered with your windows partition during QT parted YOUR WINDOWS IS SAFE. Linux merely rewrites the MBR ( Master Boot Record, used to find out which OS should be booted first and also the order of booting). Mepis does not give the option of booting other OS by default first. instead it will show a boot screen shpowing available OS es and thier booting order. usually it waits for ten seconds before booting into Mepis unless you select windows .( other distros such as Fedora, Mandriva, Ubuntu etc give you the option of selecting the default first boot OS)
Finally double check your Cd
GOOD LUCK THIS TIME.