You need at least two components:
First, you need something that does "feature" extraction, i.e. that takes your items and extracts the relevant information. For example, "new and shinny" is not as relevant as "500Go hard drive" and "seagate". A (very) simple approach would consist of a simple heuristic extracting manufacturers, technology names like "USB2.0" and patterns like "GB", "RPM" from each item.
You then end up with a set of features for each item. Some machine learning people like to put this into a "feature vector", i.e. it has one entry for each feature, being set to 0 or 1, depending on whether the feature exists or not. This is your data representation. On this vectors you can then do a distance comparison.
Note that you might end up with a vector of thousands of entries. Even then, you then have to cluster your results.
Possibly useful Wikipedia articles:
- Feature Extraction
- Nearest Neighbour Search
