I know how to create a text layer and set its contents and font
tell application "Adobe Photoshop CS3"
activate
set doc to make new document
set textLayer to make new art layer of doc with properties {kind:text layer}
set contents of text object of textLayer to "Hello, World!"
set font of text object of textLayer to "GillSans"
set size of text object of textLayer to 24
set position of text object of textLayer to {4 as inches, 1 as inches}
set justification of text object of textLayer to center
set stroke color of text object of textLayer to {class:RGB color, red:255, green:0, blue:0}
end tell
How can I have part of the text layer be in a different font? For instance, in the example above, how would I make the word hello be in a bold version of a font?