Up until version 20, Pro E had version numbers (e.g., version 12, version 19).
Then around the year 2000, they started calling the new versions Pro E 2000i, followed by 2000i2, and 2001.
Back about 4 years ago, PTC started working on the biggest change ever to the software, and internally they called the project Wildfire. At some point, instead of calling the new release 2003, they decided to go with the name Wildfire (or Pro Engineer Wildfire) instead. Wildfire 1.0 is the current release, and some people think of it as version 23 (or is 24?).
Wildfire 2.0 is the next release, available in beta version (some places may have it in pre-production already), and I believe it's release date is in March.
Software review by Bart Brejcha - Images courtesy DESIGN-ENGINE|EDUCATION
> Battle of the Bands CAD shootout between 1 Pro/ENGINEER Wildfire - 2 SolidWorks - 3 Rhino & 4 Alias Studio ... 150 people get together to discuss which is better and how to use the tool by watching industry professionals model the ACCO Swingline stapler in all four programs. Download the models for your viewing pleasure. http://www.design-engine.com/stories/battleofthebands.htm