I'm having the same problems as you. There are, however, a bunch of tutorials about the most basic tasks in XSI on the net. Menu's and all that. It's hard if you don't know where to start though.
I can make a basic shape and edit it some, but wouldn't know how one goes about making a spaceship for sins..

Didn't know that one. Thanks. Will definitely check it out.

I won't go into texturing tutorials as there are plenty of good guides already out there, suffice to say that when you get used to it, it is really simple - I can UV map a fairly complex model in about two to three hours usually. Depends on what method you use and what kind of geometry you are dealing with.

But, since I also had trouble with figuring out how to do hardpoints on a brand new mesh, here is the procedure:

In XSI you use null objects for the entire process. First, you have to create a null object called "rootpoint". After you do that, you must create a null object for every weapon hardpoint, exhaust, position light and other particle effects your ship will be using. These have to be named properly, for example, "weapon-0", "weapon-1", "exhaust" etc. - the names are going to be referenced in the .entity file of the ship using your mesh.
This is important - the converter strips first five characters from the name of your null objects. So if you just named your null point "weapon-0", you would end up with "n-0"; therefore prefix five characters (any) to the names of your nulls.

Aside from weapon, exhaust and position lights, SoaSE models also use points for "center", "top" and "aura" values. I assume these are used for various particle effects like buffs, debuffs, level-ups and so on, but I am not sure on this one, its just a guess on my part.

After you have positioned your nulls at the desired places on the mesh, you have to establish a parent-child relation between them and rootpoint null. To do this simply press 8 to open the scene explorer and drag all the nulls to the rootpoint.

Select the mesh and all nulls, export them to dotXSI and convert using the mod tool. Voila! Your brand new hardpoints are all set up.

When I started modelling years ago, I remember the first thing I did was try to make a cube. That was in 3DMax back then. I still do that today in fact. First thing I do, is make a cube. If you check out models (actually, a model, the second one is in making) I am making for the Last Stand mod, they are all shaped and grown from a cube. Its one of the simpler, but effective methods of modelling, no matter which program you use.

And don't forget to assign tangents to your model, or your texturing will look weird and lighting will be totally off!

Ok, to the OP: if the mesh is already mapped, all you need is to edit the texture files. I assume the skin texture is already all set, just make sure the alpha channel is all white. The data and normal texture formats are pretty well explained in the .pdf file that comes with the Forge tools and in any case have more to do with your favourite image editor than XSI. But if you got specific questions and/or problems (for example, what exactly is wrong with your texturing), feel free to ask, I'll help as best as I can, and I am sure others will too.

Also, the credit to hardpoint configuration process should really go to StealthCat, he was the one bright enough to actually figure it out, I just reposted here what I learned from him.

I don't exactly understand why would you need to *apply* the textures in XSI? If the mesh is already mapped out, click on the "Render"->Texture->Image and then click edit on the image, choose the texture file and see if it fits. That's as far as applying goes. Export the mesh, convert it and then add the texture file names data by hand in notepad. It is very likely, if you are using pre-made models, that you do not have properly formatted data and normal textures, so you would have to make them yourself, without those models look weird.

I don't know why it crashes every time you edit a material though, that's something I cannot help with unfortunately.

Thank you StealthCat. Ill give my models another go. Its not just the mapping. My models are pre-uv mapped in 3dsmax. So yes all i should have to do is point to the right texture. Max also has a problem with smoothing which was discussed in other topics. The "Tangents" as many refer to i believe are the smoothing groups in XSI (correct me if i am wrong). I need to redo the smoothing of the model in softimage as well to eliminate those weird lighting anomaly's after i import the model into sins. Hard points are pretty straight forward. Make a null, position it, name it weapon/engine/navlight-0, 1, etc. link it to the parent model and your set.

Major Stress, actually you don't need to link null points to the model. Just to the "rootpoint" null.

As far as Tangents go, you apply them by selecting your model, and going to Get->Property->Tangents. That's it.