Probably, though being behind a router's firewall will certainly help. I generally find the best thing to do is just make my own installation CDs with the latest service pack integrated, or slipstreamed, in. They're not that difficult to make, and with the leftover space on the CD you can include a few other useful things like drivers, an AV installation program, etc. So if you ever have to reinstall everything again, you can be reasonably protected before you ever have to connect to the Internet.
I would like to rebuild an XP computer from the original gold XP CD (no service pack). I'm a little concerned about doing this and having the computer connected to the Internet. However, the computer is behind a Linksys router/firewall with all ports closed. Should I be concerned about exposing the XP installation to the Internet until I get SP2 installed?