Jimmy,
You only need to consider upgrading the memory or graphics card if you intend to do things which are more processor or graphics-intensive than the average home user needs. The iMac will happily make movies with iMovie and music with GarageBand. However, if you intend to use Final Cut Pro or Logic, then upgrades would be prudent to speed up your workflow. It is possible to have a 256Mb graphics card installed when the iMac is ordered, along with a 500Gb internal disk. RAM, up to 2Gb, can be added at any time.