1. Your unsupported and unpatched environments could be vulnerable to new exploits that come out after April 2014.
2. XP may be working just fine, but it's more than a decade old. You should upgrade to take advantage of new OS technology. Better memory management for NX, better file search, improved User Interface and more.
3. Your other business applications may no longer be supported after April 2014.
In 1999, there was the fear that key computers around the world would fail and cause a global "meltdown" as January 1, 2000 approached. While there wasn't a massive "meltdown" of computer systems, many companies used this as an opportunity to upgrade their systems, re-evaluate and re-engineer their processes. I can’t think of a better excuse to modernize your PLM system than this.