Vulnerable After Install Before Updates Downloaded?

I'm about to carry out a clean install of XP. It's my first planned install - previously I've been forced into it following an encounter with the blue screen of death. So this time I'd like to do it with a little more care.I've searched the forums, and looked wider. There are some great articles out there, but some questions remain unanswered for me.I know I have to track down backup files for Outlook, Outlook Express, and Firefox Bookmarks. Hopefully, I'll work this out for myself. I will also copy all the contents of My Documents to an external HDD, of course.The main issue still on my mind is security. Presumably, once XP (SP1) is reinstalled, drivers added, then SP2, I should add my Panda antivirus suite, Spybot, Ad-Aware, & Zone Alarm. These will all be seriously out of date, so the next thing will be to re-establish my internet connection in order to update them.

Will my PC be vulnerable during this intervening period? If so, is there an alternative? Can I download the updates now, before wiping the hard drive, copy them to the external drive, then copy them back somehow before going online? Or is this regarded as an unavoidable risky time, like baby turtles trying to make it down the beach from their eggs to the safety of the sea, while predators have a field day?