There's really no need to have to buy a CD, especially if you have to wait to be paid to do so. DId you download the MD5Summer self-extractor?http://www.md5summer.org/md5v12005.exe
If not download it and navigate to the folder you saved it in. Double click the file and choose "unzip" from the list of options. Leave everything at the default values and you will now have two new files called "mdsummer" in the same folder (with a 3d version of the same icon).
Hover your mouse over each of the two MDsummer files in turn. One will say "Windows MD5 sum generator" and one will say Windows MD5 checksum container". Double click the one labelled "Windows MD5 sum generator".
In the md5 program box that appears select the folder your linux mint .iso file is saved in. Click the "Create Sums" button.
Highlight your .iso file from the list in the left hand panel. Click "add" so that it appears in the right hand panel and hit "OK".
When the program has finished computing the MD5 sum of the .iso a save dialogue will appear. Just hit cancel as you don't need it.
You should now have a line in the MD5 program box that has the name of your .iso in the left hand column and an MD5 sum in the right hand column (labelled "hash"). Check if this MD5 sum matches the sum given by the mirror you downloaded the file from.
If the MD5 sums do not match delete your .iso and download a new one.
If the MD5 sums do match burn the .iso to a CD (or DVD if you downloaded the KDE community edition) at a low speed (if your CD/DVD burning program gives you the option).