TextEdit won't make a new document with a title (at least in 10.4.11 anyway), you would have to save the untitled document as something or open an existing document. Since you are wanting a dialog to set a name with a date in it, I went for the latter approach. The following script makes a blank RTF document (well, there is some formatting stuff in there) and opens it in TextEdit:
<pre title="this text can be pasted into the Script Editor" style="font-family: Monaco, 'Courier New', Courier, monospace; font-size: 10px; padding: 5px; width: 720px; color: #000000; background-color: #E0E0E0; overflow: auto">-- get the current date text
tell (current date) to get ((its year) * 10000 + (its month) * 100 + (its day)) as text -- yyyyMMdd
tell the result to set TheDate to text 3 thru 4 & "." & text 5 thru 6 & "." & text 7 thru 8 -- yy.mm.dd
set TheFolder to (path to the desktop) -- or set TheFolder to (choose folder)
set TheName to text returned of (display dialog "Enter the name for the new document:" with title "New RTF document" default answer TheDate & " - " buttons {"Cancel", "OK"} default button "OK")
try -- create a new empty RTF document
set TheText to "{\\rtf1\\mac\\ansicpg10000\\cocoartf824\\cocoasubrtf440
{\\fonttbl}
{\\colortbl;\\red255\\green255\\blue255;}
\\margl1440\\margr1440\\vieww9600\\viewh8400\\viewkind0
}"
tell application "System Events" to get exists of file ((TheFolder & TheName & ".rtf") as text)
if not (the result) then
set TheOpenFile to open for access ((TheFolder & TheName & ".rtf") as text) with write permission
write TheText to TheOpenFile as «class utf8» starting at eof
close access TheOpenFile
else
display alert "The file \"" & ((TheFolder & TheName & ".rtf") as text) & "\" already exists" as critical
error
end if
on error
try
close access TheOpenFile
end try
return
end try
tell application "TextEdit" -- open the file and set the contents to the current date
activate
open file ((TheFolder & TheName & ".rtf") as text) as alias
set the text of document 1 to ((current date) as text) & return
set modified of document 1 to true
end tell
</pre>