Hello Dave Binko,
The following is the closest that I have come to finding something to do what you want. It was actually suggested by 'CHW803' on the Comcast Help Forums while I ('M_') was still a Comcast customer and asked the same question. The technique works very well and accounts for variations in startup times due to finalization of software/update installations, etc.
Visually See when Windows XP has Actually, Finally Booted
(i.e., see when your computer really is "ready to use" after booting/starting it)
1. Right-click on the "Start" button at the bottom-left of the display.
2. Left-click on the "Explore" menu item.
In the left-hand pane/window:
If you want this feature to be activated for all users of the computer, then proceed with all the steps below. However, if you want this feature to be activated only for the current user (the user you are logged on as now), skip steps 3. and 4. below and continue at step 5. below.
3. Go up to "All Users" (under "...(C:)", "Documents and Settings") and left-click on "All Users" to expand it (down).
4. Go down to "Start Menu" and left-click it to expand it (down).
5. Go down to "Programs" and left-click it to expand it (down).
6. Go down to "Startup" and left-click it to expand it -- it expands in the right-hand pane/window.
In the right-hand pane/window, right-click in an empty area of the window. A menu will pop up.
Select "New", then select "Shortcut" from the next pop-up menu.
When the "Create Shortcut" wizard appears, click "Browse...", click "My Computer", click "...(C:)", click "WINDOWS", click "SYSTEM32", click "taskmgr.exe", then click the "OK" button.
Click "Next>" in the Create Shortcut wizard. The name for the shortcut should be "taskmgr.exe" (you can change it if you want). Then click the "Finish" button.
When the Windows Task Manager display appears during startup, select the "Performance" tab (if it was not the last tab selected -- Task Manager remembers this). When the "CPU Usage" display settles down to about 1%-5%, all startup (boot) processes/programs have finished initializing and your computer is ready to use. On some computers, the "idle state" may actually be higher (e.g., 10% CPU Usage), depending on what is running in the background.
You can close/exit the Task Manager at any time by clicking the "X" in the upper-right corner of the window. You can later restart the Task Manager manually by simultaneously pressing the "Ctrl", "Alt" and "Del" keys ("Ctrl+Alt+Del").