what type of plotter are you using?
Xerox and Oce have FREE Plot SPOOLING SHAREWARE.
(all are on their web site to download)
If it is HP you can use SMARTSPOOL.
If you need and help let me know.
I personnaly use SmartSpool, you can use it to ANY type of printer/plotter
There is this programe whch i use to send online printings to the local print shop called Repro desk by OCE (its a freeware).
Now its true, this is a remote access programe which allows someone to dial up a server and send you drawings , but it can also be used to send drawings to your local/network printer.
And the best part is you can first preview the plotfile drawing, with line thickness, positioning, etc, before you actually send it.