>> does this syntax look ok
No. If you have spaces in your attributes you have to enclose the entire attribute in quotes. If you use double quotes to surround the attribute, you should use single quotes to delimit string literals within your attribute. Try:
[tt]
onload="window.open('index.html', 'Santas Helper','toolbar=no, statusbar=no, resize=no');"
[/tt]
instead.
>> I also have another onload command in the body section of the page. Will the two interfere with each other?
It depends on exactly where the onload directive is placed. In particular, which element it refers to. It's possible to have different onload handlers for different elements. But if you've placed both onload handlers in the <body> tag itself, then yes, they will interfere with one another. Only the second one will be executed.