Now this is HTML/CSS basics: in
http://www.bullstailgating.com/photo/themes/classic/template.html, you have
<object id="Igeo1"
classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000"
codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=4,0,2,0", width="998" height="215">
<param name="movie" value="themes/classic/images/bullstailgating banner 3.swf"/>
<param name="quality" value="best"/>
<param name="play" value="true"/>
<param name="loop" value="true"/>
<param name="menu" value="false"/>
<embed src="themes/classic/images/bullstailgating banner 3.swf" type="application/x-shockwave-flash"
pluginspage="http://www.macromedia.com/go/getflashplayer"
quality="best" play="true" loop="true" menu="false" width="998" height="215">
</embed></object>
as top banner. Wrap that into a container that is center-aligned. Replace the code I just pasted in with
<div style="width:100%;text-align:center">
<object id="Igeo1" classid="clsid:D27CDB6E-AE6D-11cf-96B8-444553540000" codebase="http://download.macromedia.com/pub/shockwave/cabs/flash/swflash.cab#version=4,0,2,0", width="998" height="215">
<param name="movie" value="themes/classic/images/bullstailgating banner 3.swf"/>
<param name="quality" value="best"/>
<param name="play" value="true"/>
<param name="loop" value="true"/>
<param name="menu" value="false"/>
<embed src="themes/classic/images/bullstailgating banner 3.swf" type="application/x-shockwave-flash" pluginspage="http://www.macromedia.com/go/getflashplayer" quality="best" play="true" loop="true" menu="false" width="998" height="215">
</embed>
</object>
</div>For such trivial HTML questions, please read up generic help (google for it!) from tutorials that explain HTML basics.
Instead of worrying about the alignement of your banner I would worry about the fact that you're running cpg1.4.16, while the most recent stable currently is cpg1.4.21. Your version is outdated and contains serious security flaws that are actively being exploited. It's mandatory to upgrade instantly to avoid getting hacked. Read up how to upgrade in the docs that come with coppermine and that are available online as well (link at top of screen).
Before you do, you should also consider reading
http://coppermine-gallery.net/demo/cpg14x/docs/index.htm#theme_create_rename to make sure that your upgrade doesn't overwrite your custom theme.