Jasper Reports is a superb open source alternative to Crystal Reports. It\'s great for single page PDF pages such as letters & invoices to multi-page reports. However it\'s
Jasper gives a Web Services API which you already have found, I suppose. For that being a Web Services using XML, it can be accessed through any language, like C# in this case, when you convert the service description (WSDL) to a service stub on that language.
On that given link there can be found Jasper Reports wsdl file locations and after having access to them your task is to create the stub, which is a code level access to the given XML interface. For Mono this can be done with a simple command line command according to this tutorial and the rest of the work is to use this code how ever you want to use it.
The exact command can be found through these two links with not much magic, but it is something as easy as one command running wsdl.exe
with the given path (eg. http://localhost:8080/jasperserver/services/repository?wsdl) as argument and then compiling the result with a command similar to mcs /target:library SomeService.cs -r:System.Web.Services
where you replace SomeService.cs with the name of the file that was the output of the previous command.
That's it!