Hi thindenim
Couple of things. You won't be able to do this as you suggest in CSS. However, two things could help. Specify the width of the <li> element in the subnav div. As you know the width of the subnav you can work out the number that can be accommodated in that width. Remember to add the padding and margins to the overall. In that way you will force any extra <li> into the next line.
Couple of other points while we are on the subject.
You haven't specified a background colour in the body code. Always good idea as not every one uses the default colours in their browsers. Also you have a non-valid style element at line377 .RecentlyViewed_Txt - vertical align not recognised.
You might also want to run your html through a validator - as round there is a missing <ul></ul>, I think after the subnavbar div.
If you want to discuss further, send me a PM and we can chat tomorrow (friday)
Regards
Ian