CDs will store ~700MB of data while DVDs will store ~4700MB of data.
VLC Player (
http://www.videolan.org/vlc/index.html) will play .flv (flash files) without a problem on Windows XP.
As for storing the MP4 videos, you can use either CDs or DVDs, though you will fit more onto a DVD.
I would NOT recommend using SD cards or flashdrives for long term storage as they degrade quickly over time and are meant for short term storage / file transfers.
For sharing, I would say use DVDs, and for long term storage you can invest in an external hard drive. The
Fantom 2TB (~2 million MB) is a popular recommendation on the forum. The external hard drive will give you plenty of space to store video files (and other important documents and data).
Here's a link to some highly recommended blank DVDs.
http://www.amazon.com/gp/product/B00...SIN=B00067DUB8
and a link to the
Fantom 2TB drive.
http://www.amazon.com/gp/product/B00...SIN=B002XITVCA
If you have any more questions please feel free to ask.
-JMP