If you registered your copy of XP, then you should be able to get a replacement for a nominal fee from Microsoft.
I don't know whether or not Vista will accept 98 as a valid upgrade option however. If any do, it will likely be the more expensive versions, but if you want my opinion, Vista is best avoided. Microsoft has already apparently pushed up the release schedule of the next Windows version for sometime next year, so given how bad Vista can be, it might be worth waiting it out to see if "Windows 7" is any better.
Can I get my Windows XP Pro CD replaced? If so, how? Or do I have to purchases a whole new operating system @ full price.
I am building a new system with new hard drive. I upgraded my old system from 98 to XP Pro 3-4 years ago. Since then, my my XP Pro upgrade CD has gotten mispacked, 3 moves in 12 months. By luck, I have found most of my CD's including the 98 cd. Or should I upgrade to some version of Vista (from 98?)