VS 2010 Image Gallery - Adding Previous And Next Button

I know a little bit of vb.net but don't know all that much about the asp.net technology. I do some volunteer work for a non profit organization and what I'm trying to do is integrate an image gallery into their site, instead of using an external image service that they use now.

After some searching I found an easy to use program that automatically creates the necessary thumbnails in a table.

However I want to add some functionality; when a user clicks an image for full size I want to add the option to click a button or link, to get to the next image.

I've done a lot of searching but couldn't find how to achieve this. I guess I need to find out the current image and then somehow jump to the next image.

How to implement this. Preferably I'm looking for something that is easy to implement. I'll have a number of different albums with a different amount of images. If possible I'd like to avoid having to rename the images so that they are photo1, photo2 etc.

Currently the image gallery looks like this : [URL] ....

I'm pretty sure I will need to make some changes to the viewimage.aspx file. Currently it only contains:

vb Code:
<img border="0" src="<%=Request.QueryString("img")%>" alt="" />

Not sure if you need to know the code that does the thumbnailing + creating clickable thumbnails, but I'll post it just in case it's needed

vb Code:
<script language="c#" runat="server"> void Page_Load(Object sender, EventArgs e){   
// Modify these numbers for the thumbnail size you want    const int maxWidth  = 200;    const int maxHeight = 200;       
ArrayList pics = new ArrayList();    string html;    int imgHeight;    int imgWidth;    foreach(string s in Directory.GetFiles(Server.MapPath(""), "*.jpg")){      System.Drawing.Image currentImage = System.Drawing.Image.FromFile(s);     

[Code] ....

I got the code from here: [URL] ....

but the contact button doesn't work, otherwise I would have contacted the original author.