The SD700 does not take Secure Digital High Capacity cards, so if you bought one by mistake, it will not work with the camera. See if the packaging has the SDHC logo on it, as shown here:
http://www.digicamhelp.com/accessories/memory-cards/sdhc.phpEven if it's not a SDHC, a 4GB card will probably not work with the SD700. At least that's what Canon implies here:
http://web.canon.jp/imaging/pssd700is/spe-e.htmlUnder the Recording Media heading it says:
"This camera has been tested with memory cards through 2GB. Use of all memory cards cannot be guaranteed."
Hopefully you'll be able to exchange your current card.