Don't have exact code with me at the moment but it works along this line using the '@' character:
MsgBox "@This text will be bold.@There will be a blank line before this text appears in normal font weight.@And another blank line before this text.",vbOKOnly,"Test"
As described it gives you one line of bold text followed then the rest in normal text. No control over colour as far as I know.
Using the "@" to format a messagebox does not work in code in Access 2000. It can only be performed in a macro. It does however work in Access 97 though.