I wanted to do this upgrade right now because I have spare time. If everything is alright in two weeks our baby will born, so I won't have much free time anymore!
It wasn't that much expensive, I purchased mobo, CPU and videocard. Everything else is the same that I had: RAM, disk drive, DVD-ROM, DVD burner, housing, PSU... I've been saving for some time, and it helped that my computer lasted for many months with the same configuration (the only upgrade was the video card).