To rename a file in XP (windows 2003 is way cooler) . Go to Run type cmd and it open a black screen called command prompt go to the location there using cd blabla place if its on same drive else change to the drive where it is .
After locating it than type rename urfile.zip to newfile.pk3 simple as that.
If u cannot find it just send me the file to my email addy i will .pk3 but wherever ur downloading that file , dude save it as .pk3 not as .zip .
OMG! that is just the most converluted way of doing it.
When you download a pk3, and you have a program like winrar or winzip on your hard drive, the download manager will default to 'run with' one of these programs - thereby converting a pk3 file to a .zip file.
If you have accidently done this, or done it without thinking, you CANNOT rename it .pk3. this will not convert it back.
1. Re-download again, this time changing it from the default of 'run with' to 'save'. This will preserve the pk3 file format
2. If 1 is not an option, you will need to pack it up again as a pk3. Therefore, download PackScape (google for it - there are loads of links).
Open PackScape and go to File > New. Now drag and drop all the files for folders from the map .zip file into the white area on PackScape.
Go to File > Save as, and change the file format to pk3, and save.