I assume you have a PC with a floppy drive, right? If so, you need to stop by http://68kmacwin.googlepages.com/winmac, a very useful page made by a fellow soldier who goes by the UN benjgvps.
First things first, download the Floppy Image Writer program on that page. I'm pretty sure this works better with an internal floppy drive, but an external one will suffice.

You'll need Stuffit Expander 5 here.

Then, you'll need the Network Access 7.5 file, which you can find here.

Run Stuffit Expander. You'll see a menu like this:

Find the Network Access 7.5 file, and drag it to the Stuffit Expander window. One of the two items you should get from the resulting decompress operation is the actual image file.

Unzip the FLW (what the image writer will now be referred to at this point), and open it up. Have a floppy disk on hand; PC floppies are A-OK.

Click Browse in Write Flopy

-Desktop (or wherever the image is)

-click on the network access image

-Open

Then, stick your floppy in and press Start and Yes.

Insert the floppy inside your SE/30. It should load correctly.

If so, open the disk and copy the system folder to the HD. Seperate the Finder from the old System Folder (drag it to the desktop and keep it there). Rename the old system folder "Old System Folder". "Bless" the new system folder on the HD by dragging the Finder out of it, and dragging it back into the new System Folder. Rename it "Temp System Folder". Restart.

Your SE/30 should restart to a bare System 7.5 install, which you can use as a platform to natively decompress System Disks.

Then, on your PC, download the PC Exchange and the Stuffit Expander 4.0.1 links in the page previously mentioned. THIS IS A VERY IMPORTANT STEP!

Open the FLW.

Click Load Image

-Desktop (or wherever else the image is)

-click on the PC Exchange image

-Open

Then, stick your floppy in and press Write Image.

The following is quoted from benjgvps himself:

Now go to your mac and put the disk in, go to your hard drive and find the system folder, then go to the control panel folder, then drag the "PC Exchange" file into the folder. Now your mac can read PC formatted floppies

Open the floppy writer program on your PC and put a floppy in. Click "browse" in the "write floppy" section and find the "stuffitexpander" image. Click "Open", Then "Start", Then "Yes".

Now on your mac go to the floppy and drag the "stuffit expander 4.0.1" folder on your hard drive (Do not drag onto the desktop unless you drag it into a folder on your desktop). To use stuffit expander go into the folder and click stuffit expander, click file and then expand (or "apple key" and "E"), then find the file you want to expand.

Click to expand...

Next, download Disk Copy 4.2 here. IMPORTANT STEP #2!

Now, copy it to a PC floppy.

Now, on your Macintosh SE/30, put the Disk Copy floppy in, copy Disk Copy to the HD, and open up Stuffit Expander. Click "File", "Decompress", and find the file you copied. Open it.

click on the resulting Disk Copy .smi when it's on the hard drive.

Disk Copy will self-uncompress and turn into the real program. Feel free to trash the compressed files now.

After that, feel free to download the system files of your choice on your PC, copy them over, decompress them with Disk Copy/Stuffit Expander, install, and enjoy!

Click to expand...