Most modern motherboards will take either DDR ram or both types though not together . Your motherboard may not need changing
The odd figure of 480Mb Ram could be due to an onboard graphics card sharing sytem RAM
It seems that if what you have is not DDR: that needs changing to a minimum of 1Gb .More is better but 1Gb with a decent graphics card is a great start IMHO
The graphics card race is really a 2 horse race , Nvidia or ATI : Agp is OK, PCI- Express better and onboard RAM:min 128Mb: The terms refer to the way the graphics card is connected to the MB and PCI-E is the newer and faster slot.
If its an onboard graphics card, I find that for graphics specific task like Photomanipilation esp with Photoshop very few of them are up to the task.
Some ATI or Nvidia onboard graphic card are OK but if they rely on shared memory their performance may prove dissapointing
These specs may all read interesting ( or very boring

) or even

( surely not...

) : what is most important is fitness for purpose: If the PC wont do what you want: the most cost effective way of getting there is the best
Could mean upgrading the specs or
Getting a better specced one
HTH
PS : I was posting the same time as pixepixel; needless to say, it is unlikely that an intergrated graphics card with such minuscle amts of shared Ram will help you with your large TIFF files in Photoshop