How to Make 2nd HDD Bootable?

Dell Dim 4600

HDD 1 becoming questionable so adding 2nd (maxtor 200g). I want to gradually move to HDD2 and eliminate the orig HDD.

I don't want to xfer (image) ALL the data from HDD1 but selectively xfer key items - am willing to re-install any programs. I (and my kids) have built up an enormous amount of junk over the years and see this as an opportunity to clean-up. Also don't want to carry and bad stuff (spyware, malware, etc.) that may be lurking (though I do use Adaware/Spybot, etc)

Can I make HDD2 bootable also so that when I disconnect HDD1 - I can make that the primary?