The info on the Netvibes pages about creating Universal Widgets via the UWA is needless complicated.
Making a searchbox with or without a aditional opions from web-based available search tools is not very difficult.
I will describe the steps I took, the difficulties I encountered, and how I solved them.
First you need to make an xml page the way Netvibes likes it.
Use the Pubmed Searchbox as template if you want a simple searchbox for one resource.
Open the link in a browser, save it on your pc and open it with Notepad
Don't forget to change the Title info and the meta name info about Author and Description
You include the seachbox and add images and links if needed. (For a drop-down searchbox you could use the NLM QuickSearchbox as template.)
Then you have to find a way to host it somewhere. (When correctly configured they can be saved as xml or html extensions. The cms of the Rijksuniversiteit Groningen does not accept these files as xml to be saved in their directories, but with an html-extension they do not complain.)
Don't forget to add a thumbnail image. This improves the first impression of the widget massively ;-). I mostly use simply PrintScreen or Snippy to make a screenshot. Paste & Edit it in Paint, save it and then upload to a server of to your Flickr account.
Additional you could add links inside the widget to embed the widget in other preferred environments.
here's a short movie demo. (Warning! It has no voice or extra explanation, so it could be just a lot of screens flipping over ..... Just give me a comment or email if you want to know more.