Dreamweaver offers customizable dictionaries for spellchecking. Start the spellchecker using Text Check Spelling or Shift+F7. The spellchecker checks the selected text and provides suggestions for misspelled or unrecognized words. If no text is selected, it starts checking at the cursor location and will optionally "wrap around" until the entire document has been checked.
Dictionaries are stored in the Dreamweaver 4/Configuration/Dictionaries folder. The English version of Dreamweaver ships with U.S. English and U.K. English dictionaries. Dictionaries in additional languages can be downloaded from Macromedia's site and should be placed in the same folder. The spelling dictionary can be chosen under Edit Preferences General Spelling Dictionary. You can add to your custom dictionary, stored in the Personal.dat file in the Dictionaries folder, using the Add to Personal button in the Check Spelling dialog box. Your personal dictionary is simply a text file that can be edited in a word-processor to add, correct, or remove words in the dictionary.
The spellchecker always checks the visible text in the Design pane of the current Document window. It can't check spelling in the Code pane, nor can it check spelling for the entire site all at once.