spend money/time on sth
spend money/time in doing sth
.with sb
就算是
被动语态中,也是用doing
I spent 2 dollars buying a book.
------Two dollars was spent buying a book.
好,补充你修改后的问题,既然是这样的一个句子,应该就可以了,这里是to作为连词,连接了两个动词,spend time和to do sth没有直接关系,就是说,并不是花时间来做这件事,而是花了时间做一件事,达到另外一个什么目的,或者做成另外的什么事情.比如,我花尽可能少的时间（做作业）来省下时间看电视.
I spent time as less as I can (doing homework) to watch TV.
括号里的等于是省略了,不说.
你应该把do后面省略号里的也打上,这样就能给你讲得更详细了.
这里的to do,和stop to do有类似的用法,就是stop （doing one thing）to do another thing.