Iomega unveiled its 750-MB Zip drive ($180) last week. It's 21/2 times as fast as its predecessor and has three times the storage space. It can read older discs and is a cinch to use. Since Zips first appeared, though, the rewritable cd (cdrw) and external hard drive have moved into Zip's territory. Do you need the 750? Depends on how much you love the format. CDRW drives can be bought for half the price, and the discs offer nearly as much storage space (up to 700 MB) for a fraction of the cost (80[cents] vs. $12.49). Moreover, Panasonic is slated to release a memory card by year's end that will hold as much as 1 GB of information. So, unless you're a big fan, skip the Zip.