Is using Time Capsule better than using an external hard drive because it won't stress the hard drives? (for using Time Machine) I just plugged in an external hard drive that has Firewire 800 and started Time Machine, but it seems that both the internal hard drive and external hard drive work frantically copying about 75GB of data from the iMac to the external hard drive.

And in fact, I dare not use the computer while it is copying that much data, as I don't want to over work the hard drive's head.

If it is the case of Time Capsule, backing up using Wireless, then won't it actually work better, because if Wireless-G is limited to 1 or 1.5MB of data per second, then it won't stress the hard drive, and user can work on anything without affecting the hard drive's hard work?

(Updated: Details: 1MB/s, instead of about 75MB per second if using the Firewire 800.  In that case, the user can use the Mac and won't stress the hard drives, especially if the Mac OS X might read 50MB at a time, and put that data in RAM (as a hard disk cache), and just pass this data to TIme Capsule by Wireless-G -- then there is no need to read any data again until 50 seconds later, if assuming the copy speed is about 1MB/s.  Would this be true?)
That last paragraph is very difficult to understand, but if I follow, creating a RAM disk is not going to help...primarily because there's no problem to fix in the first place; Your concerns are unwarranted. 

Time Capsule hard drives in particular are very low failure rate, and above that, Time Machine does not tax your system indefinitely. When the timer starts a new backup, the hard drive will spin up. On completion, it will spin down as necessary. These drives, like most of decent quality today have a high MTBF &amp; MTTF, so relax.