First, create a CSS class with the following styles:
<style>
.scrollable { display:block; overflow:auto; }
</style>
Then, apply it to the table like this:
|scrollable|k
|long|table|that|overflows|the|side|of|the|tiddler|and|need|to|be|scrolled|longerheadingtext|andmoreheadingtext|andstillmoreheadingtext|
|long|table|that|overflows|the|side|of|the|tiddler|and|need|to|be|scrolled|longerheadingtext|andmoreheadingtext|andstillmoreheadingtext|
|long|table|that|overflows|the|side|of|the|tiddler|and|need|to|be|scrolled|longerheadingtext|andmoreheadingtext|andstillmoreheadingtext|
|long|table|that|overflows|the|side|of|the|tiddler|and|need|to|be|scrolled|longerheadingtext|andmoreheadingtext|andstillmoreheadingtext|
enjoy,
-e
Eric Shulman
TiddlyTools.com: "Small Tools for Big Ideas" (tm)
InsideTiddlyWiki: The Missing Manuals