debugger complains: auto-attach to process 'aspnet_wp.exe'

[sirpelidor]

Hi, I'm a newbie to asp.net world whom just got myself a VS.net 2003 (yay).
There are alot of things I don't understand so please bare with me:

1) I made a simple aspx page with cs code-behind, when I click Debug ->
Start (F5) it complained: Auto-attach to process 'aspnet_wp.exe' on machine
'(my machine name)' failed. Error code 0x8013134b

2) When click Build -> Build Solution, Output shows: Build 1 succeeded, 0
failed, 0 skipped

3) If click Build -> Build (project name), Output same as above.

4) If I just go ahead and run that aspx file at by typing the
localhost/.....aspx it just worked.

Here are my questions:
a) what's diff between "build" and "debug"?
b) my useraccount is part of administrator group, yet my debugger still keep
failing
c) i even changed my machine.config file <proceesmode> username to
administrator with password, yet it kept failing, maybe its not User Right
related issue?
d)why was I able to see the web page I created without clicking build /
debug !?

p.s: sorry spam a brunch of questions at once, but this is my first time
using some kindda IDE interface and I'm being throw off by all these options
and choices.

thank you